Depends on whether it is a traffic control sign similar to speed limit or stop signs or a caution or information sign. If the former I'm all for obeying the sign as it is my legal obligation to do so. If the later I use my best judgement. Whether that is good judgement or not I guess is up to the results.

If the word "please" is on the sign it sure does set my mind in a more compliant mode. Like last summer at Confluence Park in Denver there was a sign asking cyclists to please dismount and proceed as pedestrians. I thought following the sign was the courteous thing to do. Until the next trip and the sign was still there and there were no, nada, pedestrians; in which case I rode right on through since I had no legal obligation to comply with the sign.