How do I or you deal with people who sit in your reserved seats on the train?

I mean like those who won't budge from your reserved seats and if the train is crowded and your can't get a another seat or can't get a member of staff.

I just need some ideas, maybe a subtle revenge like I don't know like putting itching powder down their back, I know thats lame but it's frustrating me and I'm afraid of it happening again so I need ideas that will make me feel more at ease.

I know someone will prob say let it to or don't let it get to me but it's not fair, I mean I can't shout at them or force them off their seat as then the people on the train will look at me as the bad person, especially if it's a lady with kids.
How do I or you deal with people who sit in your reserved seats on the train?
Post Opinion