I agree with what others have said, that the netnews, two way pager
gateways, and mailing lists are all substantially the same, except for
one key thing: in the case of mailing lists it WILL be possible in some
way for those systems to preserve the signature, should they so choose.
It's possible in all cases, should the gateway choose to encapsulate
the incoming message inside a MIME message/rfc822 wrapper or the like,
but that's not going to be very useful in practice.
News gateways and mailing lists are similar in that a signature might
survive either in some limited simplistic cases, is unlikely to
survive either in a more realistic general case, and we have no
consensus about whether that's a problem, or if we have any advice to
offer beyond recommending that the gateway or list add its own
signature on the way out.
So my suggestion continues to be that we should note that gateways are
rarely transparent to DKIM and leave it at that.
NOTE WELL: This list operates according to