Brazil pastes small (postage-stamp-like) sticker receipts for payment next to the visa itself. Mine has three: one for $100, one for $20 and one for $10. (They're actually preprinted for that many Brazilian reais, but I paid US $130 for it.) The visa seems secure but the stickers fall off on both my wife's and my passports. Both visas were issued at the same time by the same consulate, so this happening to both of us may not indicate a more widespread problem.

I reglued mine, though I suspect it wouldn't invalidate the visa if they're not there.