Clarification:: Why not <code>/bin/true</code> or something else, what about <code>systemd-logind</code>?

Also, I think RHEL 5 and 6 do not have this command, so probably need to pick something else?

Or are you using this just as a sentinel (i.e. marker) value to detect elsewhere? If that is the case, I'd suggest make it more obvious, like <code>@!@!@!SENTINEL!@!@!@</code> so there is no confusion.