Any evidence would be ambiguous.
Wasn't there a brief controversial news story
within the past 20 years of some astronomer
claiming to have detected DNA in interstellar clouds?
Obviously, peer review quickly dispelled the claim,
if the story is correct,
but it reinforces the idea that any evidence
that is circumstantial, indirect and not gathered
"in situ" would be unreliable.
An ambitious Enceladus mission with a lander-rover,
possibly fitted with a microscope [like the MER's?], etc., would be
required.