Can Forgotten Signpost be played as an action or does this card already have to be in base to use its ability during a showdown?

"Forgotten Signpost" is a Gear card with the ability: "[Action][>] Exhaust a unit you control, [T] : Move a different unit you control to the location of the unit you exhausted to pay for this ability."

1. Can it be played as an Action? No. The [Action] keyword on "Forgotten Signpost" is attached to its ability, not the card itself. Therefore, the keyword grants permission to use the ability during a showdown; it does not change how the card is played. As a Gear, it must still follow the standard rules for playing Gear (e.g., normally playing to your base per Rule 148.1.a.1).

2. Does the card have to be in your base to use its ability? The ability is on a piece of Gear. Gear is a game object while on the board (Rule 148.1.a). There is no specific rule stating a Gear must be at a base to activate its ability; it simply must be on the board and legally positioned. Per Rule 150.2, activated abilities of Gear are restricted to your Main Phase during an Open State, unless they have a keyword like [Action] that provides an exception. Because this ability has the [Action] keyword, it can be activated during a showdown.

Note: I could not fully verify this ruling against the retrieved rules.