This will make your logs robust to (e.g.) running under ARM or x86 architectures.
My logs are already robust regardless of the architecture (notwithstanding that I have to translate from OCaml custom integers to local ones), as long as it is assumed that the signal numbers logged are those corresponding to the local system (which is a very natural assumption).
Using names would actually be less robust in this use case, because other programs reading these logs (not under my control) expect numbers and, even if they could also understand names, there are no standardized names for signals, even considering only the local architecture.
Using names also suffer from the possible introduction of errors when upgrading stdlib (if the Sys module add new names and new conversions, then my program will miss those without a compilation error since those are not defined in a sum type (why?)).
Using names would indeed be more reliable in case those logs were copied into another arch and/or read by humans, but this is not my use case.