Looking for generic OID to transmit free-form text in an SNMP trap

I'm looking to do some custom monitoring of a system and the contracted NOC
only supports pings, SNMP queries, and SNMP traps. My first choice was to
send an e-mail and have their system ingest it, but that's not possible, and
the first two aren't an option, which means I'm looking to send them SNMP

What OID should/do I use for sending traps with free-form text? Do I just
use sysDescr? Or is there another OID that's recommended?