I know what you mean I dont play in groups also and when I get a Heroic most of the time I just dont do it at all or wait to level up so I can solo it later because I never get other players to go with me, its like there are too busy or just dont do Heroics at all... but when it comes to flashpoints everyone wants to do those so theres no problem finding people there
And i agree it would help alot to give some kind of hint to let people know its a Heroic... that way i can just walk right by the mission giver lol