[SirAndy]

Originally Posted by Gustl

that's it - exactly

you anserwed your own question :-)

I agree. We usually just use a white or yellow marker on the rim.

One thing we learned the hard way, don't mark the valve on the tire!
Because freshly mounted tires actually rotate on the rim when you are taking off and your mark ends up somewhere other than where the valve is.
Always mark it on the actual rim ...