A tee marker was uprooted, so I stuck it back in the ground and teed off. Penalty?
Possibly not, but we wouldn’t recommend doing that again. Let course officials (the “Committee”) sort it out. If you were deemed to have gained an advantage by playing from the place you determined to be the teeing ground, the stroke-play penalty is two shots. In match play, if you and your opponent disagree where to tee from, you can make a claim before either of you play from the next teeing ground, and the Committee would resolve the dispute. It’s the same if you had le the marker and estimated the teeing ground.