The tag is present in Lintian version 2.104.232. That is the most recent version we know about.
Running this shell script with the shell's -n option set fails,
which means that the script has syntax errors. The most common cause of
this problem is a script expecting
/bin/sh to be bash checked on
a system using dash as
sh -n yourscript to see the errors yourself.
Note this can have false-positives, for an example with bash scripts using "extglob".