I can honestly say i had my tag licks ready last week when fretmentor assigned them, but i can't take credit for them. I had gotten them from a guitar website i subscribe to, in their bluegrass section. They call them licks, but they can be tags. I have 2 D licks, 2 C licks, and 2 or 3 G licks. They sound cool when played properly at full speed (i haven't achieved that yet)
I think they are too long for a tag, in fact, i would consider these runs, but they could be modified for a tag. I think a tag should be around 10 notes max. Anything more, and you're playing lead guitar.
Don't know if you guys ever noticed, but there is a little G tag in "Will the Circle"...

What's the website?

gotta play 'em man ...just pick it up and play

Is it possible that a tag lick could be anything other than the designated lead so that the others in the group would know that the end of the song has arrived?

Yup, that's the point.

Do you mean that another person beside the one playing lead can play a tag lick signaling the end of a song? confused.