Ideally take the reg from the bottle but some these days you can't.
Make sure your marker is stripped down i.e. barrel is off and it's not attached to the bottle, see first point.
Don't tell them, when we first started flying to Mill Series we were a bit wet behind the ears and declared it, then after a few flights we just stopped telling them.
So there you go, and, your markers should be in the hold, not held as hand luggage.
Maybe Scottish Warriors being huckled into a meatwagon in Glasgow Airport's not a bad thing.....
Sid