Thanks Kakejiku. That is exactly what my Sensei wrote when he looked for this signature. He told me that this pot was not Tokoname pot.
Ok, I did a little, actually it was a lot of search terms on google.co.jp and this site gave me some pretty comprehensive information.
http://www.gasen.jp/
株式会社 雅山(がせん)
代表者:長谷川 雅也
約900年の伝統ある山形鋳物を受け継ぎながら、新しい息吹を込めて、製造・販売しております。
■製造・営業品目
銅・鉄・合金および鋳物、茶の湯道具・花器・美術工芸品およびインテリア作品。
■銅構造物・建築用・庭園用装飾作品/モニュメント・銅像制作。
■通商産業省認定 国家指定伝統工芸品。
What it says (short and abbreviated translation) is there is a company called 雅山 Gasen, that is run by Masaya Hasegawa (born 1959). It has about a 900 year history in Yamagata (prefecture) casting and molding. Perhaps you could e-mail directly and see if they are the one that made this...but it might be a stretch because they are more into working with bronze and sculpting They did have some beautiful flower vases that appear to be ceramic though...info@gasen.jp
Hope this helps and is not a dead end.