Signets are used to signify groups of characters that work well together, even reaching across cultural boundaries. Indeed, some cards with the same signet can all be viewed as if they were labeled with a unifying Unloaded Keyword such as Ranger or Besieger. It is thus no coincidence that the four signets center around particularly important characters, with those Characters or cards unique to them activating various signet abilities. Usually, however, (and this is true of Unloaded Keywords in general) signets are not something to be overly concerned about unless there is a particular signet-targeting ability that is going to be exploited.

Three of the signets (Aragorn, Gandalf, and Frodo) were introduced in the very beginning with the release of The Fellowship of the Ring, while Theoden was introduced in The Two Towers (naturally). Particularly general wording in the rulebooks suggests that more were planned, but following the end of the Movie block signets were dropped entirely, their space replaced with an icon indicating personal Resistance instead.

Below are four cards each bearing one of the four signets in their lower left-hand corner. From left to right: Gandalf, Aragorn, Frodo, and Theoden:

And here are four of their counterparts, cards that can activate to benefit (or be benefited by) those with particular signets:

It should be noted that there is no rule stopping a character from boosting himself with a signet-targeting ability, such as if Theoden, Lord of the Mark were to grant himself Defender +1 using Forth Eorlingas! above. Indeed, most signet abilities have at least the option of boosting the signet's avatar, so if one of the four signet characters is a major part of your deck's strategy, these abilities can be used to great effect.

As noted above, following Movie block Companions were no longer printed with any signets at all, and no more cards having costs or effects affecting only signeted cards were made. However, there is a curious case in that some cards were reprinted in later sets, notably Boromir, Defender of Minas Tirith and Pippin, Hobbit of Some Intelligence. Both of these cards have the new Resistance icon in place of a signet, but since they are word-for-word reprints of an earlier card, it was ruled that they both have the Gandalf signet of the originals. They are therefore unique in being the only signeted cards not actually bearing the signet on the card itself.