Can a linguistics check to detect a forgery be made untrained

[Thaine]

Linguistics is a trained only skill. Detecting a forgery is an opposed linguistics check.

Can you make an opposed linguistics check to detect a forgery without being trained in linguistics?

[Entryhazard]

Linguistics wrote:

In addition, you can also always attempt to detect a forgery.

It's from the Core Rulebook at the end of the skill description

[DM_Blake]

Yes.

SRD, Skills, Linguistics wrote:

Trained You must be trained to use this skill, but you can always attempt to read archaic and strange forms of your own racial bonus languages. In addition, you can also always attempt to detect a forgery.

So you roll a d20+INT to oppose the Linguistics check the forger rolls (his will be d20+ranks+INT and +3 if it's a class skill) so your chances are slim, but you can certainly try it.