[rollnloop]

Is it possible to actually padlock a plane without having the big triangle show-up?

it is, but not directly

1/padlock (triangle appears, useful to know who is padlocked when there are many in sight)

2/use key/button "change icon type", press a few times, and voila, padlock without triangle.

note: this is as i remember it, just cannot test it works right now, hope there's no mistake in my memories.