When I was building my computing stack out of x86 machine code I noticed that even if my high level language only had signed numbers (I'm still pretty brainwashed by C, which leads to the conclusions of OP), I still needed the ISA's unsigned jumps to deal with addresses (which can have the MSB set). So my big "insight" was to name unsigned comparisons "address comparisons".

https://akkartik.github.io/mu/html/mu_instructions.html