I'm pretty sure I read somewhere that the the off-field stickers can be for individual achievement/service, but that the on-field stickers are only for accomplishing team or group goals.
The reason the players voted to get rid of the stickers in the first place was because they didn't want to emphasize individual achievement anymore, so they only brought them back as a way to signify participation in accomplishing team and group goals, such as the whole defense holding a team below "X" points, etc...., not things like an individual player getting "Z" tackles.