Here and there you see merchants who have sidewalk signs. Many merchants lock them to something solid so they won't lose them to damage, theft or wind. Locking them to post and rings is not only a big annoyance to cyclists, it is also illegal.
The best thing you can do is call this number: 416-39CYCLE (416-392-9253) and the city will send by-law officers to inspect the post and rings and remove the signs if necessary. They will impound the signs and the merchants will have to spend $200 to retrieve them.
If you feel bad for the merchant you could perhaps warn them that you called the city. But you might also want to avoid a confrontation so don't do it if you think the merchant will verbally or physically lash out at you.
Sidewalk signs are in a grey area of the law, but what is clear are keeping post and rings available for bike parking. They are city property, not private.