About street signs along 10th Avenue North and why the lettered side streets are labeled with quotation marks. Above is the sign detail that guided the design of the signs. I have asked and will continue to follow through. My guess is that it is used to distinguish the "initial" from the "direction" so that if the street is a vowel, a word is not formed. I have looked through FDOT's handbook and haven't found a reference to this. You can check yourself. I'll let you know if I find out more.
I would suggest that in the meantime one should concentrate on other things, as this does not rank as one of the most burning issues of our time.