Makers’ marks

[mklotz]

This is a nice visual of one of the construction methods using only compass and straightedge...

http://www.mathopenref.com/constinpentagon.html

There are a few instances of the use of pentagons in metalworking fields. Pentagonal valve actuators on fire hydrants are commonly used to prevent tampering and many police shields are five-pointed.

The only septagonal item I've encountered is seven-pointed police shields. Some jurisdictions seem sensitive about offending Jews by using an hexagonal form.