Meaning of "sig! N" self-signature

[Kara]

====

I've received a key with two userIDs (identify and keyIDs changed):

     uid  Dummy Name <dummy at gmail.com>
     sig!     N   12345678 2007-10-29  [self-signature]

     uid  Dummy Name
     sig!         123456789 2007-10-19  [self-signature]

====

Question 1:  In the first userID's self-signature what does
             the "N" indicate?

Question 2:  And how would one generate such a self-signature.



Timestamp: Sun 04 Nov 07, 0852 Local (UTC -0500)

====