The tag is present in Lintian version 2.104.328. That is the most recent version we know about.
Lintian has detected the presence of a #DEBHELPER# token in the listed maintainer/control script. By default, dh_installdeb will remove the token when it makes a substitution in a script.
Please note that dh_installdeb does not substitute the #DEBHELPER# token in udebs.