::It's common on business cards and nowadays in email signatures.  Since the EIT is a governmentally regulated professional certification, it's appropriate to do so, just as it's appropriate for a lawyer to style themselves Jane Doe, Esq.; an accountant John Doe, CPA; or a full engineer Alex Smith, P.E.  Plus, when chambers of commerce or business magazines/newspapers compare the "size" of an engineering firm, almost always the comparison is based on the number of PEs and EITs employeed.