+1 VHB Tape & silicone, with backer vinyl/painted alum/acrylic on reverse-side of the glass to "hide the mess". some people just use standard black/white vinyl, but I prefer to use the matching color of the
sign....painted vinyl if need-be. We inline the backer by about 1/8", as to not see it sticking out past the
sign perimeter when viewing from the front & at an angle.
keep the VHB tape to the perimeter, let the silicone fill the middle. this way, when it comes to removal, you'll/they'll only have to get a blade/scraper around the edges of the panel, and then twist the
sign panel off the glass to sever the silicone adhesive.