Can you please help ID this pottery item? Thank you

[robinsonct]

Hello and thank you in advance for any assistance you can offer in identifying the maker of this pottery planter(?).

It is 6-sided, nicely glazed, 8.5" long x 5" wide x 4" tall and about 2 lbs. 6 oz.

Thank you again!

[8838edward]

The characters appear to be "koo san" followed by a pattern number??    Can not tell if this is the potter's name, kiln name, or what.  Sorry.