like many Italian brandnames, Gi-pi-emme is just the phonetic spelled out initials G-P-M in the Italian language, and GPM is the name of the firm.
There are probably dozens, but here's a couple that spring to mind
Duegi (due-G, or two-G: G.G.)
Biemmezeta (BMZ, bi-emme-zeta)

But some defy the trend: ITM (Italmanubri) didn't go there, nobody agrees on what to do with 3TTT (Tecno Tubo Torino)