[Mobile-Portable] question about mobile QSL cards...

[Jeff, Julie, Annabelle, and Nicholas]

OK - I've searched long and hard on this marvelous invention from Al Gore 
called the Internet, but I can't find an answer to this particular question 
about making my mobile QSL cards.  Should I put my callsing as KF4KWO/M, or 
am I ok with leaving the callsign KF4KWO and then noting (as I have been), 
"...confirming a MOBILE QSO with (your callsign here)"?  For the CQ WPX 
contest in March, I did put KF4KWO/M.

And here's another thing - do the recipients of my cards want my location 
while mobile?  If they're going for WAS or if they're county hunters, of 
course they will.  But what about someone who just likes to have a card?

What I'm after here is what is 1) required by rule, 2) what is the accepted 
custom, and 3) what makes it easiest on the receiver of my QSL card for 
his/her records.

Thanks in advance for your replies.

73,
Jeff, KF4KWO
Odenton, MD
jjannanik@comcast.net