I have just looked at the battery that came with my 40d. It weighs 78.8g and the spot is colourless. The number is different though - mine says 7YGC so i guess that this is some sort of serial number. The blue label is different it looks as though it has been redesigned.
The weight is probably the most telling factor here.
A quick Google search found this link and the following reply to the original question. You may be in luck if you contact Canon
Possible counterfeit / fake canon battery - AVForums
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Just an update for you guys and anyone else wondering about Canons policy on counterfeit products....
I received this email from Canon this afternoon:
Dear Customer,
Thank you for your email.
In order for us to verify the authenticity of your product can we please
ask you to send the battery to the following address:
Alex Dodge
European Intellectual Property Manager
Canon Europe Limited, 6 Roundwood Avenue,
Stockley Park, Uxbridge, Middlesex UB11 1JA,
United Kingdom
We will replace the battery with a new one if you can provide us with
the battery, packaging, all invoices and names and details of where you
purchased the product and refrain from contacting the shop directly.
Thank you for your cooperation.
Best regards,
Canon Web Team