This would be possible with a bit of code.
If you want to only use custom properties, ShapeSheet -- built-in Visio
features sans code, then it would be difficult. You *could* make shapes turn
red based on no-test. This would require manipulations of the FillForegnd
cell using the StrSame(ShapeText(),"") expression. Still not an end-user
feature.
You could also play with the Color by Values add-on. Go to: Tools > Add-ons
Run Add-on > Color by Values. Perhaps you can get it to notice "no text".
I just took a quick look and it looks like it deals mostly with numbers, but
perhaps a quick look at the help file will yield more ideas.
--
Hope this helps,
Chris Roth
Visio MVP
www.wanderkind.com/visio