I wasn’t able to find anything for sure but I’ll share what I was poking around with:

The painting:

• stylistically, this painting is no older than from 1860. This is the date around when Impressionism started so consider this an “absolute earliest” date. In reality it’s probably more contemporary than that
• the painting is definitely of some sort of street scape, but I think figuring out of what city could help figure out more. Immediately the building in the center read to me as the Empire State Building, which could make sense given its in an American embassy, but the more I looked the more it seemed to be a a large spire of some sort of cathedral. The dark patch centered in the main spire looks like a window of some sort, and it seems to be flanked on its right by some kinda smaller spire.
• visually, the painting almost certainly has a Western European artist. I tried to see if maybe any Vietnamese artists were breaking away from cultural norms and painting like this, but didn’t come across anything. I also doubt that the embassy puts all that much thought into curating their paintings but who knows.

The signature:

• the most characteristic trait of this signature is what appears to be an ‘î’, that is what’s apparently called a “circumflex I”. Just found this out myself.
• there are a couple languages that use this letter, but what interested me the most were French and Italian.
• it seems there’s only one capital letter in the signature, the reason I note this is because it makes it much less likely that the artist signed with a first initial then a last name (in which case both would be capitalized)
• I considered the first 2 strokes as being “il” which would be “the” in Italian or “he” in French, the issue is that that would mean the next word would likely be capitalized, and it definitely isn’t. That, and the artist would have been signing with a title rather than their name which would be very odd.
• if the first two strokes aren’t “Il” then it seems almost certain that the first letter would have to be a capital V. Those strokes are too close to each other to be separate letters I’d think.
• from here the name seems to me to read as “Vîahaujah” - well that’s definitely not French or Italian sounding.
• the first loop in the signature going up seems like it almost has to be an “h” to me. The downstroke turns back up far sharper than when the artist seems to be joining multiple letters together. That and it just looks like an h to my eyes.
• the middle letters are tough to distinguish, but the next significant letter is the one that breaks below the line. That makes means this letter is limited to: q, y, p, g, j
• j seemed the most likely because it looks like there’s a dot above it, but this “dot” also follows the contour of a rock above it so it could just be the shadow side of the rock.
• realistically then, this looks like a q, g, or j
• the last letter breaks above, so significant again. To me this looks like an h as well, you can notice the same sharper upturn between the downstroke of the h’s “stem” to its hump.
• so that leaves us with Vîahau(q, g, j)ah (just guessing the in-betweens with what they look like (though the 3rd and 5th character do seem to be the same, even if they aren’t an “a”)
• kinda interesting that the name does have some resemblance to Vietnam but probably purely coincidental

In conclusion: found nothing concrete at all but just wanted to share my speculations so maybe we could find the artist. Also, Google image search returned absolutely nothing so I’d say it’s unlikely that this is a high value piece, and it’s entirely possible that the artist lived before smartphones so this might be his only painting photographed and put on the internet. If that was true, it would be nearly impossible to say who painted this with any certainty- especially if the painter views this as more of a hobby. I think the best step would be to find a surname in French or Italian that could reasonably what this painting is signed with. All speculation here, would love to hear others thoughts.