Razorblades are a pretty old far-left tactic to punish those who would dare take down their stickers.

Coming from someone who takes these down whenever I run into them (edit: lefty stickers in general, never ran into razorblades though): don't bother with fingernails. Takes forever and the stickers often tear. Use a thin piece of metal, like a broken putty knife. Coins and keys work too in a pinch to get one side of the sticker started.