Well I looked it up. I cant figure out the exact cite, but it is burried below the table of frequencies in 90.20
(e) Additional frequencies available. In addition to the frequencies shown in the frequency table of this section, the following frequencies are available in this service. (See also § 90.253.)
....
(5) A Police licensee may use, without special authorization from the Commission, any mobile service frequency between 40 and 952 MHz, listed in paragraph (c)(3) of this section, for
communications in connection with physical surveillance, stakeouts, raids, and other such activities. Such use shall be on a secondary basis to operations of licensees regularly authorized on the assigned frequencies. The maximum output power that may be used
for such communications is 2 watts. Transmitters, operating under this provision
of the rules, shall be exempted from the station identification requirements of § 90.425. Use of frequencies not designated by a ‘‘PP’’ in the coordinator column of the frequency table in paragraph (c)(3) of this section, is conditional on the approval of the coordinator
corresponding to each frequency.
(e) Additional frequencies available. In addition to the frequencies shown in the frequency table of this section, the following frequencies are available in this service. (See also § 90.253.)
....
(5) A Police licensee may use, without special authorization from the Commission, any mobile service frequency between 40 and 952 MHz, listed in paragraph (c)(3) of this section, for
communications in connection with physical surveillance, stakeouts, raids, and other such activities. Such use shall be on a secondary basis to operations of licensees regularly authorized on the assigned frequencies. The maximum output power that may be used
for such communications is 2 watts. Transmitters, operating under this provision
of the rules, shall be exempted from the station identification requirements of § 90.425. Use of frequencies not designated by a ‘‘PP’’ in the coordinator column of the frequency table in paragraph (c)(3) of this section, is conditional on the approval of the coordinator
corresponding to each frequency.