I would say that if it doesn't say class 10 on it (the icon with the 10 in the circle) then it's not class 10.

By the way, I went to the Sandisk website on your behalf because I was curious, and asked the help bot how to tell if your card was genuine. The advice it gave was "The best way to ensure you are purchasing an authentic SanDisk product is to buy from an authorized SanDisk reseller." I thought this was a really dumb answer and I told them so. Here's the question that I sent them on the web form:

I'm trying to help someone who is having trouble with a SD card and is concerned that it may be a fake. I came to your website for help making that determination. The advice given is "The best way to ensure you are purchasing an authentic SanDisk product is to buy from an authorized SanDisk reseller." THIS IS THE DUMBEST ANSWER EVER. The question is about a product already purchased, and the answer is about a future purchase. STUPID. Furthermore, your website is unnavigable. It tells us to go to the product page, and select support options for it. But if you click "support" you get back to the answer I complained about above (so the user is going round in circles) and if you click on "FAQs" then you get ALL 723 FAQS with no sorting at all - which is no use!

And I did get a nice answer from a guy called Liam, who said:

Dear Andy,

Thanks for emailing SanDisk Technical Support. It is our goal to make sure you have all the resources you need to get the most from your product.

I Understand that you want to check the authenticity of your product.

We really apologize for the inconvenience, I can really understand that you could not able to get the information on website. In this case to make a final judgment on its authenticity, you would need to send us pictures of the product for review.

Also, Povide the following information to review your warranty status and to register the product

1. Your Phone Number, What all is written on the face of the card?
2. Product code written on the face of the card
3. Your complete physical address (No P.O. Box please)
4. From where did you purchase this product?
5. Exact or approximate Date of Purchase of the card in the format of MM/DD/YYYY
6. Was card included in the packaging with the phone or device (bundle deal)?
7. How was the product packaged at the time of purchase?
8. Did the packaging have some other company name and logos on it

Please feel free to contact us.

In other words, they have no customer tools to check authenticity, but they will help you if you send them photos of it, plus the other details.

I notice that you live in America; the others on here usually recommend buying from B&H or Adorama, don't they? That would seem your best option, as they understand photography and the needs of the photographer.

However, if your card really doesn't have that logo on it, then I think it's simply a case of "not as described".

I actually have a lot more to say on this, but it'll have to wait for another post. I need to find a photo I took of a unit in a store.

I ONLY buy cards from B&H. They have the best prices on legit cards, and the legit cards are legit. 

All of mine are "stick on" decals, but they have a "quality" look to them.  I got one SanDisk 2GB card that was a "freebie" with an order and it would not even format.  The label had a very "cheap" and somewhat "ill fitting" look to it, so I think someone got slipped a "counterfeit" card.

I ONLY buy cards from B&H. They have the best prices on legit cards, and the legit cards are legit. 

Oops..I think I may have accidently clicked on report user on your tab.  I saw a message about IP or what not.  If so, I appologize ahead of time.

Anyhow...
I was gonna  ask if you have high settings like qscale or something on your camera?  Im using the same transcend class 10 card as you and it lasts until the 4 gig.

my transcend and pny class 10 cards only record for like 15 seconds at a time.  I have a sandisk class 6 that will record til full.

I have a transcend card and I have recorded for 4+ minutes without problems. Never tried going any further than that. When my card does have a buffer issue and stops, it is always within the first 2-3 seconds.

I'm not quite understanding the issue. The Amazon ad looks like a genuine Class 10 SanDisk,

the exact same one as at B&H:

http://www.bhphotovideo.com/c/product/677598-REG/SanDisk_SDSDRX3_016G_A21_16GB_Extreme_SDHC_Memory.html


The Amazon ad states:
Compatibility: Compatible with all SDHCTM and SDHCTM UHS-I supporting host devices.

One Amazon reviewer claims:
The limitation of this card is that it normally operates at 20MB/s and only achieves 30MB/s in the few devices that support UHS-I.

Then there is more information about these cards here:

http://forums.dpreview.com/forums/readflat.asp?forum=1023&message=38676177&changemode=1

Now, I do not know why anyone says the card is a Class 6 - which as far as I recall means 6MB/s.

This seems to come down to changes in technology, marketing, and people's understanding of the product. All of that is beside the point of where to buy the cards. I do not see Amazon doing anything different than B&H on this particular ad. Of course, that does not necessarily mean that you are more or less likely to receive a counterfeit from an Amazon transaction. Any such fraud would not intentionally be perpetrated by Amazon, I'm sure, but the supply chain there is far more dynamic and risky.

All of mine are "stick on" decals, but they have a "quality" look to them.  I got one SanDisk 2GB card that was a "freebie" with an order and it would not even format. 

Excuse me for hijacking this thread but I'm worried.  Do you have to format all cards before you record video?  I have only dabbled a little in video but the results were not so good as the video was "jumpy" and didn't seem to keep up with the audio.  Almost like a buffering problem.  But then again I thought it was just my old, slow laptop or the players I used didn't have the correct codec.  Now I'm wondering if I was suppose to format 1st?!