Actually, there is. Look at ITU-T Recommendation Q.763, the Calling
>Party Number information element. It includes two bits:
>Screening indicator
>0 0 reserved (Note 2)
>0 1 user provided, verified and passed
>1 0 reserved (Note 2)
>1 1 network provided
>NOTE 2 - Code 00 and 10 are reserved for "user provided, not
>verified" and "user provided, verified and failed"
>respectively. Codes 00 and 10 are for national use.
>These are also included in ISDN signaling to the subscriber. Now
>whether telcos ever bother to screen is a different question. (I
I don't have copies any more, but I am very sure the Telcordia (Bellcore, back then when I worked with them) interworking standards for Q.931 to SS7-ISUP, as well as the various Generic Requirements for switches, required those bits to be set to "0 1" if the calling party number was provided by customer equipment. I participated in at least one test where a network element failed because it did not correctly implement this, in fact, and then could not be connected to an ILEC network.