The other day, my daughter asked me where “Mind your P’s & Q’s” came from. I don’t have any idea. What does it stand for? Any ideas?
It comes from back in the day when they actually had to use those type-things, I don’t know what they are called. Sort of like raised letters on a block that you had to fit into a frame to make a page. I’m sure you’ve seen them. Anywho, p and q look very similar and it was a problem if they got them mixed up. I don’t know how, but it was. So, it became a phrase to mean “watch the little details”.
Sorry…that probably wasn’t the detailed answer you were looking for, but it’s a start, right?
Mister C has already answered this one:
What’s the origin of the expression “mind your P’s and Q’s”?
Looks like an answer to me.
You are correct. Typeface is reversed, so a typeset “p” looks like a regular “q” and vice versa. The admonition is a reminder that the letters are reversed so don’t forget that and put a “q” where a “p” goes, or as you said “watch the details”.
my mother always told me not to go out with a girl who didn’t mind herpes and q’s. 
untateve, try writing it “herpes and queues.” (After all, why would you date a girl who liked to stand in line?)