I agree with the tape choice. There are several different strengths of 3M tape so look at the labels and choose accordingly. On the consumer VHB's they list the weight they will support.
I prefer
Loctite Power Grab (aslo at Home Depot) for the adhesive. It is important to use both a tape and some type adhesive even on interior installs. When it gets warm the adhesive on the tape can allow heavier signs to slide. I used this combination recently on 1/2" thick plex letters on a plex background and couldn't get them off.
The 3M VHB is so aggressive that you better make sure it's positioned correctly because you rarely get a second chance to reposition. To increase those odds I use small squares of tape with thick dots of Power Grab on either side of the pieces of tape. This method helps keep the tape from making contact until you press on the letter. The thickness of the stroke will determine the size and thickness of the Power Grab dots. Too much and it will squeeze out, too little and it won't keep the tape from sticking until you ready.
If the adhesive squeezes out, wait until it dries before you try and clean it up.
