I started a new job recently and I noticed one day that my American flag sticker had been removed from my truck's window. I am heavily suspicious that it may have occurred while I was at work, and would further indulge in saying I believe it was someone from my building.

How would I go about handling this situation? My first guess would be going to the security desk and ask if the cameras caught anything. Since I am a contractor, I don't know if I should report it to my company's HR department, or the company I'm currently working for's HR department.

Additionally, would it be wise to purchase another sticker, and should I inform my site's manager?