Italian - signature. It does not mean firm as in company (azienda, ditta) or as in solid (solido, rigido) or as in fixed (fermo).
Delivery dude: Salve! Your new mattress has arrived. Householder: Do I need to sign for it? Delivery dude: Yes. It's a very good one. Our firm guarantees top quality. Householder: I'm so excited; I've always wanted a firm mattress. Delivery dude: I'm very happy for you. Do you think we can work another meaning of firm into this phoney conversation? Householder: I've a firm mind to do so.