When you kong over random desks at work.
I'm busted.
And my friends do frequently do this:

You know you're a traceur/traceuse when...
...you meet people (or are walking around at work, or waiting for the shuttle, etc.)and you look to see what sort of shoes they're wearing, to try and spot if they might be into Parkour (or if the shoes themselves might have merit).
...you suspect someone's shoes might be good shoes for Parkour, and you ask them if you could see the sole...
..."trying on shoes" at the shoe store includes putting your foot up on the wall to see how much it'll slide and/or streak.
...your roommates leave it up to you to change all the light bulbs in the house.
...you play "lava" on your way to the laundry room.
...you intentionally wait until the last minute to leave for work so that you can use Parkour to get there on time.
...you feel a connection and friendship with people you've never met, or only met a handful of times.
...you still love playing tag, but your friends don't like playing with you.