Ever driven down a San Diego street and noticed the bicycle under a double chevron logo on the road surface? That's a 'sharrow', and it doesn't designate a bike lane. A lot of local cyclists dislike the thing because they think that that's the city's way of copping out of making proper bike lanes for cyclists to ride on.
Park Blvd bike lane
Having a proper bike lane on major streets would be even nicer, of course - as long as it isn't Thursday where much of the bike lanes would be occupied by garbage dumpsters that people put out in the morning before going to work and wouldn't be back to wheel them back into their yard/alley until they get home late in the evening. In the meanwhile they just sit in the bike lane blocking two wheel traffic, forcing cyclists like me into the car lane.
A bike lane on trash day
When widening the street to add a bike lane isn't quite an option, tho, I like seeing sharrows on the street to remind the cars to keep an eye out for us skinny little two-wheelers, too.
BMUFL sign on 6th Ave
It's even better to have periodical Bike May Use Full Lane (BMUFL) signs along with the sharrows on the roads. I don't think cars notice the signs by themselves as much. Many drivers I've chatted with say they notice sharrows more than they do white street signs like the BMUFL ones. It would be nice if drivers in general look out for bicycles more. Then perhaps many cyclists won't be scared off and do things like riding on the sidewalk, where they become even harder for cars to spot than the ones riding on the road.
How not to ride a bicycle
Then, of course, there are some idiot cyclists who will just do what they want regardless of how unsafe it is for them and for others... like running traffic light or riding against traffic (on the wrong side of the road). No sharrow or sign or bike lane can save dodo's like that...