Given that not all employees have a diamond:
All Stack Overflow employees aren't given a moderator diamond; the Community team has tightened up internal policies regarding who gets one and who doesn't. [...] — Anita Taylor
can we have some visual indication that they are an employee?
This was previous requested back in 2011, but declined. However, the situation appears to have changed now with fewer employees being given a diamond.
That way when they post on a meta site we know that it's somewhat "official".
Failing that please ensure that everyone includes the fact they're an employee in their profile given that this request to add employee to their profile pages was also declined.