I see these signs all over the city, but I don't think a lot of drivers have ever taken the time to read one. It's a pretty dang simple concept, if a bicycle is in the right lane going slower than the auto traffic and you want to get by, then simply change lanes and pass.
Don't sit behind me and honk your flippin horn!
Sometimes I feel like deliberately riding my bike up and down one of these streets just so I can point out the sign to everyone who honks. Maybe some of them will read the sign and figure it out.