The numbers are usually a vinyl adhesive product.
They can be removed without damage using plastic single edge razor blades to lift and peel the vinyl and "Rapid Remover" spray and paper towels to remove the adhesive residue.
Both items easily available on Amazon...
The numbers are assigned by the club to current members, and should only be displayed by legitimate current members...If you want to display numbers, please join the club.
Rich, KE4GNK/AE, Overkill Engineering Dept.
'The Silver HamShack' ('07 International 22FB CCD 75th Anniversary)
Multiple Yaesu Ham Radios inside and many antennae sprouting from roof, ProPride hitch, Prodigy P2 controller.
2012 shortbed CrewMax 4x4 Toyota Tacoma TV with more antennae on it.