Among traditional shamans in Siberia there is no such rule. In fact, shamans are often introduced by their title. In a shamanic society, being a shaman is not an unusual thing. It is an occupation much like a doctor, teacher, or public official, so there is no need to make it a big, mysterious secret. In fact, because they serve their communities, a shaman is a public figure.
When someone is first initiated into becoming a shaman, it is a great public event. The community helps make the new shaman’s robe, drum, and other equipment. The ceremony lasts for days.
Shamans often wear indicators of their position. Throughout Siberia one can often tell who is a shaman by looking at their boots. The Nenets, Selkup, Nganasan, and Evenk nations all decorate their shaman boots with spiritual designs or stain them with red ochre.
Buryat and Evenk shamans often wear mismatched boots. This is not only to show that they are shamans, but to confuse the spirits when during ceremony, they switch the boots to the opposite feet.
Shamans often wear different clothes or hats as well. Even in the city wearing Western clothing, shamans can often be identified by wearing a protective toli mirror or talisman.
Shamans are given seats of honour and are treated with great respect. In the days of Chinggis Khaan (Genghis Khan), shamans did not have to serve in the military.
In conclusion, there is no rule in Siberia that prevents shamans from calling themselves “shaman”. The only taboo is a non-recognized shaman trying to make that claim.