The term showing of interest, as used in this Chapter, shall mean a designated percentage of public employees in an allegedly appropriate negotiating unit or a negotiating unit determined to be appropriate, who support the filing of a petition or a motion to intervene. Any showing of interest must be accompanied by a declaration of authenticity as set forth in section 201.4(d) of this Title. A showing of interest may also be used to determine whether an employee organization is entitled to certification without an election pursuant to section 201.8(c)(1) of this Chapter.