My rotor housing are marked with a flourecents pink f on the front one and r on the rear one. I can see this under my spark plugs. Do this mean the engine has been rebuilt?

 

Stock engines have F and R stamped on the rotorhousing top surface, facing drivers side, about 3" above the "Mazda 13B". This is normal.

Anything else almost has to mean it has been apart at least once. People generally don't write on engines for the hell of it, unless it is junkyard writing/marks, but this doesnt sound like that. Junkyards often mark mating surfaces and bolt heads to ensure you don't swap parts on them and then return bad ones. Besides, most used engines with any mileage at all on them are too dirty to clearly write on.

You can spot mazda remans by abnormally shiny silver rotorhousings and front cover (painted), a sticker on the oilpan, and a red coating on the tension bolt heads. Some remans in the last 2-3 years have had a tag on the front cover, and some of the newer oilpans have an extra drain **** on the side, near the front.