Read your cite again: "Similarly, a statement from the bureau that “[i]t is common for federal law enforcement agents to identify themselves to citizens simply as federal law enforcement.” However, the director of the bureau [said]… “I probably should have done a better job of marking them nationally as the agency.”
So, they are supposed to ID themselves as Federal agents, and in general, what agency. Only if you are detained, questioned or arrested do Federal agents have to give their names. The BoP officers dont wear nametags on their uniforms, this is a special dispensation.
Now in certain cases, plainclothes are not required by LAW to identify themselves at Officers, but they run a risk by doing so : A unanimous Seventh Circuit panel in Doornbos v. City of Chicago (2017) stated that, “[a]lthough some unusual circumstances may justify an officer’s failure to identify himself in rare cases, it is generally not reasonable for a plainclothes officer to fail to identify himself when conducting a stop.” Thus, there is some chance that an officer could be denied qualified immunity on the basis of a failure to identify if that failure was deemed unreasonable and precedents just discussed had “clearly established” a right to disclosure. Additionally, whether or not a law enforcement officer has identified himself or herself prior to effecting a stop or seizure has some influence on how a court interprets a criminal defendant’s subsequent actions."