As a condition to the issuance of a sign permit as required by this chapter, all persons engaged in the hanging or painting of signs, which involves, in whole or in part, the erection, alteration, relocation, maintenance, or other sign work in, over, or immediately adjacent to a public right-of-way or public property if used or encroached upon by the sign hanger or painter in the said sign work, shall agree to hold harmless and indemnify the City, its officers, agents, and employees from liability for damages resulting from said erection, alteration, relocation, maintenance or other sign work.