I tend to get a litte carried away with the structure of my signs. I like to think that there is no such thing as too strong. I also don't like failures or call backs.
Most shops I know use 15-20 lb high density urethane as a substrate for their projects. In our shop we use no less than 30 lb Precision Board HDU. The number refers to the pounds per cubic foot. The higher the number the stronger and more durable the product. I also like to use a sturdy structure inside our sculptures as well when the situatiion fits, most often a welded steel frame. Making things extra sturdy lets me sleep at night without fear of a possible callback or failure down the road.
For the Town Crier Whiskey sign I am adding an arm, hand and bell. Chances are someone will give it a pull down the road, most likely more than I would like. So I welded up an armature from 5/8" steel rod and then glued this deep into the high density urethane sign. No way ths was going to fail!
As I looked at the sculpt today it occurred to me that although my first sketch looked a little like George Bush, the Town Crier now looks a little like Prince Charles frrom certain angles. Funny how that worked out. Maybe it's the ears?
Once the glue had cured I set about sculpting over the bell handle frame. No one but me would ever know it was there and that was OK.
Everyone else would be looking at the outside and admiring the pretty face. :)