We've done it plenty of times... some customers hate holes. VHB tape should hold up fine. Just dont treat it like a simple tape and slap job -
Scuff the surface, clean it with alcohol... use a heatgun to warm it, apply the tape and apply pressure for a good 20-30 seconds.... Re-heat the sign/surface a little, and it should be ok.
.080 aluminum weights 1.2 lbs a sqft aprox. 3 SQFt...so 3.6 lbs. 8.5" per 2 LB roughly. I'd likely VHB Around all edges, 84"... or close to 20 lb strength.
Of course these are all best case scenarios - A cheap painted drywall will likely peel if you put 20 lb on it. But if you go around the edges, pre-heat and scuff with a brillpad or something, then reheat. you'll be fine.
Is it ideal? No... Nothing beats mechanical fasteners, but reality is not every job can be mechanically fastened. Is it going to fall off? doubtful...
If you're really concerned, throw some PL max on it. You can apply PL in -12 celcius... just be aware it's going to be a permanent bond, you'll likely tear the paint off the aluminum if they ever try to remove the signs. Let them know this will be it's new permanent home. You'd be amazed at how people would rather a permanent bond glue that will likely damage their wall a lot more than a screw would. Then summer hits,and they want it positioned in a new spot...
https://www.lepage.ca/en/lepage-pro.../pl-construction-adhesive/pl_premium_max.html