Good idea but I think putting the trailer registration (lic. plate) number on the roof would be more specific and more 'cop friendly'. 

"FREE SAMPLE"

As a precaution I put my race car number on the top of my enclosed trailer. 36” in black on a white trailer top. May not help but a police helicopter would give me a fighting chance. Bought the vinyl numbers from a circle track numbers supplier on line. 

56 Vic, B'Ville 200 MPH Club Member, So Cal.

It didn't mention anything about the 72 hours on the Apple site. But if that turns out to be true, then they wont be alerted to it straight away, which would be good.
I would want to see something in writing to be sure. Though I couldn't imagine anyone not telling the truth just to sell you something. 

Samantha said it’s an anti-stalking feature.  Anyone that the airtag is not register to will get an alert after being in constant contact with it for 72 hours.  So if I wanted to see what bars Vic is hanging out at I could put a tag on his T-Bird 🤣

I’m not sure but I thought Samantha told me that won’t happen until 72 hours have past. Hopefully if something gets stolen you could track it down before the 72 hours. I’ll have to double check with her

Hi Larry. 
Great piece of information so I just had a quick look on the Apple site.
It appears there is a bit of a problem though. To stop people tracking other people, if the other person has an iPhone and it detects that the tag is travelling with them and sends them an alert and starts making a noise. I cut and pasted the info below from the Apple site.
AirTag is designed to discourage unwanted tracking. If someone else’s AirTag finds its way into your stuff, your iPhone will notice it’s travelling with you and send you an alert. After a while, if you still haven’t found it, the AirTag will start playing a sound to let you know it’s there.

I’ve always been on the lookout for a way to track my truck/trailer when traveling in case of theft.  But I’ve always found the options to be too expensive or too short of range.  Samantha found me a simple, affordable new device by Apple called Air Tags.  It’s a small disc about the size of a quarter that is easy to hide inside your truck, trailer or racecar.  You can track the disc on your iPhone or iPad.  If someone steals your vehicle, every time the disc passes another iPhone or IPad it updates the discs location and sends the discs location to your iPhone/iPad.  Best Buy and the Apple Store sell them for $30 each or 4 for $100.  There is no annual fees and the battery lasts about a year before needing replaced.  Check it out!  Larry Short