Howdy,

While there is no legal requirement to sign anything after your  
callsign, here's the deal anyway.

Bfore (I think) 1978, you did have to sign mobile or portable, as well  
as the call district you were mobile or portable in. For instance, if  
you were driving your car in Oklahoma, you might say "KB8TYJ portable  
5". This is no longer required. You don't even have to tell the FCC if  
you're going to be away from your home station for an extended period  
of time.

Having said that, "mobile" and "portable" are actually defined. Some  
people I know believe "Portable" means "using a handheld radio" (i.e.  
walking = portable), but that isn't so.

The second and third scenarios are correct: you don't have to sign  
with anything extra. However, if you choose to do so, "portable" means  
"at a specific location that is not your home station location". Thus,  
being parked in an RV park overnight would constitute "portable".  
"Mobile" means "In motion, or at an unspecified location", or  
something like that. Thus, if you're driving your RV, or are stopped  
at a Wendy's or a gas station, you're mobile.