It's super simple. Get the police to investigate - go to the nearby business owners and ask them if they placed them or know who did, and remind them that lying to the police is a crime much worse than placing the blocks.
They can as easily fine a business for not removing the blocks as for placing them, and it's not like there's a question about where the blocks actually are.
It's more a matter of how far you're willing to go.
The block has flowers painted on it, it’s pretty. Why can’t I park a block on the public street?