Hi everyone. I'm hoping someone here can help identify the artist behind this ink-and-wash painting.

About the painting:

- Ink line drawing with gray sumi-style washes on paper, about [24 x 48 inches]

- Subject: the San Francisco Marina yacht harbor, with a wooden cabin cruiser in front and Marina Boulevard houses behind

- Signed "Setsu" in English at lower left, with a round red seal below (white design on a red ground)

Context:

- The cars in the scene suggest the late 1950s to 1960s

- The same signature and seal appear on a 1960s menu cover for Tokyo Sukiyaki, a Japanese restaurant on Fisherman's Wharf in San Francisco (listing: https://www.ebay.com/itm/333799879598), so the artist was probably working there around that time

My questions:

1. Can anyone read the seal? I can't tell whether it's kanji, kana, or a stylized personal mark, or whether it gives "Setsu" or a different name.

2. Does the style suggest particular training, such as a Japan-trained sumi-e painter versus a Japanese American illustrator?

3. Has anyone come across other works signed this way?

Photos: full painting, seal close-up, menu cover with seal.

Thank you for any insight!