It really depends on where you are going and your comfort level. I would say that if you are asking the question, the answer for you is probably no.

We don't have a very good network of connected protected bike lanes, and some roads that are vital to get from one place to another are not at all safe.

But, there are routes that are protected and other roads that are pretty safe, so if you happen to be able to use those it can be pretty great.

I don't know if there are laws about locking to street signs, given the number of bikes I see locked to street signs probably not.

I use Grove St Bicycles.