EasyDiscuss signature in ES search results

I am so afraid of creating forum threads by now.

I wanted to modify the search results and have profile informations inside these. This worked with the 'HEADLINE' on this way:

echo $user->getFieldValue('HEADLINE')

- WORKS

This worked like a charm. But when I try to take the discuss signature, it stays blank and gives no result.

echo $user->getFieldValue('DISCUSS_SIGNATURE')

DOES NOT WORK

I thought that maybe the difference is, that the EasyDiscuss signature is an app compared to the headline, but I have no clue, why calling this function does not work the same way.