The owner of a billboard sign and each user thereon shall indemnify and hold the City harmless from and against any loss, claim or expense (including attorney's fees, publisher's liability and advertiser's liability) arising, directly or indirectly, from the erection and/or use of said billboard sign, and such owner and user shall maintain liability insurance in accordance with, in an amount to be approved by the City, except that the minimum insurance for publisher's and advertiser's liability shall be five hundred thousand dollars ($500,000.00) per occurrence, one million dollars ($1,000,000.00) aggregate.