gnus-treat-highlight-signature

gnus-treat-highlight-signature is a variable defined in `gnus-art.el'.
Its value is

(or t (typep "text/x-vcard"))

Documentation:
Highlight the signature.
Valid values are nil, t, `head', `first', `last', an integer or a
predicate. See Info node `(gnus)Customizing Articles'.

You can customize this variable.