Had one in a shop I worked at. All they got for suggestions to improve productivity was... FREE BEER. Fun part, it was in 15 different handwritings..... Odd.....lol Box was gone in one week.
I will never submit a suggestion anonymous or not for any company because i've seen too many times that someone would suggest something to increase productivity and to get their wish but with increased productivity everyone's KPIs went through the roof and people hated them for the change, and I've seen suggestions end up costing someone their job because their boss/owner felt threatened by the initiative. my current company has mandatory anonymous job/boss surveys we're supposed to fill out quarterly (online "anonymous" form) and every time they're a few people short and I guarantee you I have never filled one out and I never will.