You could also just write your own signature:
def lazy_user (auth = self): return auth.user_id reference_user = 'reference %s' % settings.table_user_name def represent(id,record=None,s=settings): try: user = s.table_user(id) return '%(first_name)s %(last_name)s' % user except: return id self.signature = db.Table(self.db,'auth_signature', Field('is_active','boolean',default=True), Field('created_on','datetime', default=request.now, writable=False,readable=False), Field('created_by', reference_user, default=lazy_user,represent=represent, writable=False,readable=False, ), Field('modified_on','datetime', update=request.now,default=request.now, writable=False,readable=False), Field('modified_by', reference_user,represent=represent, default=lazy_user,update=lazy_user, writable=False,readable=False))