I've seen bikes removed from street signs [by the city] so I wouldn't suggest it, but I also overall don't suggest locking things to street signs are they are often "removable" at the base...

regarding safety other users all shared commentary similar to how i feel. on the one hand a lot of delivery people are on e-bikes on the streets every day and reported bike fatalities are not astronomical. on the other hand my experiences with drivers here has been terrible so I could never openly say it's a reasonable method of transportation for the general population