It may be just a sticker to counter radiation, as @Andy Yan said. I tore off the the sticker there was just some black slippery substance coated. There was nothing like the stickers on clothes bought from few stores. (So its not the RFID sticker @davidgo)
But, I browsed about such type of stickers, 'Anti Radiation Sticker' there were no supporting blogs or comments about its use found, other than on the sites selling them. Then why the company itself using them? I couldn't understand.
Visit the link, advocating uselessness of Anti Radiation Stickers
Edit - Its not a 'Anti Radiation Sticker', it absorbs dissipating heat, made from graphite while ARS are made of metal.
(Thanks to @AndyYan)