Hi Frank,
Yes, it would be very helpful to be able to sign transport files as well.
I was looking into this extensively as a means to license ABAP based products as well and have seen many "dark horses" on customer sites (most of them generate subroutines and some tried to hide the code).
I think that something like SSF can easily sign the file if TP supports it for the "add to buffer" but I never followed it further as I cannot imagine it supporting any validity parameters or external object keys (trial versions, etc).
We solved it within ABAP itself. Statement LEAVE TO TRANSACTION helped a lot.
If SAP code could be signed and imported only if original then I would certainly support it! If SAP offers an SSF framework for signing parter ABAP code then I will very gladly share my ideas and support it as long as TP does not become unstable (there is quite a lot of namespace complexity in upgrades now-a-days...).
I will open a seperate thread for this (we are hijacking Teddy's thread... :-))
Cheers,
Julius