I agree with a more discrete sign and a real doorstop. However, if somoeone does try to enter and cannot, then maybe that would violate the supposed safety code and get you in trouble. Can you clear it with the boss first?
Ideally, you would be able to drive to work in a van and then go out to the van, close the curtains, and dilate. Or if you have a pickup truck with a rear window, a bed cover and a little mattress, plus window coverings and one of those things that runs the ac or heat back there through the rear window, should see you through.