Increasing bike ridership in a country built for cars also means increasing numbers of injuries and deaths caused by careless drivers.
That is especially true at intersections where cyclists heading straight come into conflict with drivers looking to make a riqht turn.
In the last few years - Portland being the best known - have started installing “bike boxes” at signalized intersections give cyclists a safe place to wait for the signal where drivers won’t be able to miss them. That takes bikes out of the side lane where drivers often queue up to make a right turn and usually focus more on oncoming traffic than whether the bike lane is clear.
San Francisco has begun installing bike boxes as well, but where Portland and other cities instruct drivers to “WAIT HERE” just beyond the bike box, San Francisco has taken a different approach to letting drivers know how to use this novel new traffic control device:

Got it?
Did you even see the sign?
Let’s try this again:

Even if you did notice the sign and you recognized it was a traffic sign, despite the fact it is printed wth a non-reflecting material, using a template similar to what SFMTA uses for Muni information and announcing community meetings, would you really have time to follow a diagram with the instructions set in 48pt type?
Would you be able to do it while in a car or on bike while negotiating Market Street’s five-way intersections and minding the traffic turning off to the right while also coming to a safe stop at the intersection?
While sign is correct in that “cyclists stopped in bike boxes are easily seen by motorists, improving safety at intersections” the unmarked bike box and instructions only readable by pedestrians aren’t contributing to improved safety. But wouldn’t it do more to improve bike safety to simply write “Wait Here” where you want drivers to wait?