Car signs

I think this is a long shot but won't know until I ask.  First let me explain. I have always driven a Jag and always had magnetic car signs. I now have a 2005 Vandenplus and find the doors are made of aaluminum. Guess what.. Magnetic signs will not stick  to it. I'm curious to know if anyone else has come up with a solution for this short of permanent paint which I'm not going to do.

I'm a real advocat of always wearing my name tag and car signs. Can't even tell you how many great leads I have picked up from both. I miss the car signs but not about to give up my ride for them..