12950.  Every person licensed under this code shall write his usual
signature with pen and ink in the space provided for that purpose on
the license issued to him, immediately on receipt thereof, and the
license is not valid until so signed, except that if the department
issues a form of license which bears the facsimile signature of the
applicant as shown upon the application, the license is valid even
though not so signed.



12951.  (a) The licensee shall have the valid driver's license
issued to him or her in his or her immediate possession at all times
when driving a motor vehicle upon a highway.
   Any charge under this subdivision shall be dismissed when the
person charged produces in court a driver's license duly issued to
that person and valid at the time of his or her arrest, except that
upon a third or subsequent charge the court in its discretion may
dismiss the charge.  When a temporary, interim, or duplicate driver's
license is produced in court, the charge shall not be dismissed
unless the court has been furnished proof by the Department of Motor
Vehicles that the temporary, interim, or duplicate license was issued
prior to the arrest, that the driving privilege and license had not
been suspended or revoked, and that the person was eligible for the
temporary, interim, or duplicate license.
   (b) The driver of a motor vehicle shall present his or her license
for examination upon demand of a peace officer enforcing the
provisions of this code.



12952.  A licensee shall display his driver's license upon request
of a magistrate or judge before whom he may be brought for violation
of any traffic law.


12953.  In any circumstances involving accidents or violations in
which the engineer or any other crewmember of any train is detained
by state or local police, the engineer or any other crew member shall
not be required to furnish a motor vehicle operator's license, nor
shall any citation involving the operation of a train be issued
against the motor vehicle operator's license of the engineer or any
other crew member of the train.



12954.  Section 12951, subdivision (a) of Section 15250.5, and
subdivision (a) of Section 15250.6 do not apply to a person who has
been issued, but does not have in his or her immediate possession, a
currently valid and appropriate class driver's license or restricted
driver's license for the operation of firefighting equipment and who
is operating that equipment wholly within this state under the
conditions described in subdivisions (a) and (b) of Section 21055, or
is returning from the scene of the emergency or other situation
described in those subdivisions.