ASTM E2659 Standard Practice for Certificate Programs does allow certificate issuers to grant a designation and/or associated acronym to certificate holders. (It does not encourage it, by the way.)
This has been controversial and I do understand why some certifying bodies do not want certificate issuers to issue a designation. However, when we were developing the standard, what we consistently heard through the stakeholder community is that if a standard forbids designations completely, then many in the community will just ignore the standard and the accreditation program (which will both be voluntary). This means programs can continue to use any designation they like, including calling certificate holders "Certified." This gets us nowhere.
So, we determined to allow designations to be used, BUT NOT designations that use "Certified" or similar, confusing words. For example, for the Institute for Organization Management, graduates use the IOM designation which really isn't confusing with certification, and that would conform with the ASTM standard. On the other hand, if a certificate issuer issues a "Certified XYZ", that is confusing, and it would also be a non-conformity (not allowed under the standard).
Here's the actual portion of the ASTM standard related to this issue:
7.1.2 A certificate issuer may grant a designation or designation acronym or both to certificate holders only under the condition that the designation and/or designation acronym granted shall not include the words "certified," "certificated," "licensed," "registered," or "accredited" or in any other way imply such statuses.
We felt strongly that preventing ALL designation use would just further splinter the industry and those with certification-implying designations would simply ignore the standard. Allowing designations with the appropriate safeguards increases the likelihood of broad adoption of the standard while at the same time prevents the use of confusing designations.