The Forest Ave. Hannaford by Back Bay isn't my normal grocery store but I was in there the other day getting a few things when I noticed this little piece of metal attached to one of the back wheels.

At first I thought it was a device to keep the wheel clean but then why wouldn't they be on all four wheels? I went on with my shopping and didn't give it another thought until I saw (and actually read) this:

Genius! So I guess we have Hannaford to thank for not seeing rouge shopping carts throughout that section of Portland anymore.