marking .forward

Is there any harm in doing something like the following so that procmail can
know whether a message came to it via a .forward pipe as opposed to some
other non-interactive means (like a cron job, an aliases file, or whatnot)?

 "| IFS=' ' && exec /path/to/procmail -f- DOTFWD=yes || exit 75 #username"

Is there some other way that already exists?