Why can't you leave them on the sidewalk, then, where they can still be seen by cars?

I almost get his here once a week when it's rush hour. I saw a woman pushing a stroller almost get hit last week. Is that worth whatever shortcut you're taking?

The signs are designed to sit in the middle of the street, to remind drivers to yield to pedestrians at crosswalks. Their placement on sidewalks would obstruct the pedestrian right of way. There are no short cuts being taken.