v=$(
	${SH} -c 'trap "echo ok; exit" USR1; kill -USR1 $$' &
	# Suppress possible message about exit on signal
	wait $! >/dev/null 2>&1
)
r=$(kill -l $?)
[ "$v" = "ok" ] && { [ "$r" = "USR1" ] || [ "$r" = "usr1" ]; }