As Andrew points out I have posted this question elsewhere and I thought you might be interested in the following.
A big thank you to Billy of Nicekoi for coming up with the answer to this thread when he saw it in
www.koi-ireland.co.uk. Through Andrew, of Selective Koi, Tomoko in Japan says:
'This word comes from the three families of the Tokgawa house in the Edo period (1603 to 1869). It means Triumvirate, the big three.
GO means honourable
SAN means three
KE means family
The families' names are Mito Tokugawa Ke, Owari Tokugawa Ke and Kii Tokugawa Ke'
Thanks to everyone who took time to look and post on this thread.
Hilary