A few factors affecting this when I’m making the decision is
how is it hung?
how is it mounted?
how much area has been cut out of the piece ?
multi-layered?
Normally I use 14 gauge
.100 is a good start for signs but again it would depend on all the things previously mentioned. Aluminum will still oxidize so depending on what kind of look you want you may have to coat it or wax it or something as well.
I understand your comments regarding how the sign would be mounted vs a hanging sign to take into consideration on the thickness. Makes sense.
Will check on availability of powder coating services.
Regarding amount of detail, here is a sign that I am presently designing to give some perspective. Multi-layer red letters screwed onto background via threaded offset spacers (1/2”) welded to back of letters.
I do a lot of multi layer signs as well. One recommendation is to do a full size back plate so you get good color contrast with the entire sign. You can even do multiple colors. Here are a few I have done. I use mainly 14 gauge as well.
Just to throw in my two cent opinion, I also do a lot of multilayer, multicolor, detailed signs. My go to plan is 16 gauge foreground with 18 gauge background. This strategy helps keep the weight down and I still can get good detail in the 16 gauge.
Feel free to change the text and re-use the top portion. I also made a hanging portion for across the bottom. You can see it standing against the garage door. That’s why the loop feature at the bottom were added.