Because you're still on DEV?

run this in debug console

hint str productVersion;

what does it say?

Did it actually download the update, or did you launch it straight away?
Have you tried verifying game cache? Is development branch actually off (IIRC, if you press Escape, settings are not saved)

It appears when you open "Camera" while playing mission.

This needs a high priority.

I just spent 20 minutes downloading the regular version to record a video, and the watermark was still there.

I found out that it appears after you exit the splendid camera.

"["Arma 3","Arma3",104,111745,"Stable"]"

http://img801.imageshack.us/img801/8392/9gw9.png

Now that I'm at it, it'd be nice if the watermark wouldn't appear in the dev build if "Steam Friendly UI" is enabled. Would allow me to record machinimas using the dev build, instead of having to spend 20 minutes switching every time I want to record or play.

I also have this problem. It happens when using the "SPLENDID" camera.

@MulleDK19 in the meantime you can remove it yourself http://killzonekid.com/arma-scripting-tutorials-how-to-remove-beta-watermark-other-things/

Updated ticket. Still persists with 1.06 stable.