Marconi Wireless Telegraph Company Stock Certificate (1913) with Signature of Former Belfast, Ireland Lord Mayor William George Turner

Hello Everyone, I have a Marconi Wireless Telegraph Company of America stock certificate. The scans of the front and back are included along with of picture of it in its frame. It appears to have been purchased in 1913 by the broker Billet, Campbell, and Grenfell. In 1920 it was bought by a man of the name William George Turner whose signature is on the back with Oxford,St Belfast next to it. About a month after he purchased it, the stock certificate was cancelled due to the absorption of Marconi into the new formed company RCA (I believe that's why there are a bunch of punch holes throughout the certificate). I did some research and found out he was the Lord Mayor of Belfast, Ireland from 1923-1928 and was Knighted by the Royal Crown in 1924. I also found out he had an interest in wireless communication and was mayor of Belfast during the broadcasting boom throughout Belfast and Britain during the mid 1920s. Also of note, he was fundamental to the formation of the Belvoir Park Golf Club in Belfast. I researched the price of these Marconi of America stock stock certificates without any historically significant signatures and they seem to range from $50 to $100. How much do you think the presence of the Mayor's signature will increase the value? Overall, I am happy with my find and have enjoyed researching the history behind it. Thanks for the input.