The value of the album alone entitled Try Rod (note, not Rob) McKuen in the Privacy of Your Own Home is an average of $7 - $20 on today's market. With his signature, it is $70 - $100. There is not a huge market for forging Rod McKuen's signature, so the likelihood is high that the autograph is authentic. The best method for determining such would be through Heritage Auctions, which can be done for free through their website: www.ha.com
Just checking in to see if you viewed your answer and if you are seeking further assistance?
Please let me know.