Are you trying to figure out what that thing is, or to actually find the shutoff? The shutoff is most likely just outside the edge of the street pavement. Mine is in the utility strip between curb and sidewalk.
Being that old, I would first turn a sink's cold faucet wide open in the home and have someone on a phone watching it. Then, while the person that is outside operating the valve is on their phone, they should turn it closed ...slowly.
If while doing so and it does not affect the water flow to the home faucet that is running inside the home as it is being shut off, I would not shut it off tightly. (especially on a weekend when plumbers charge OT and even double time).
Because just by a chance it is the homes water shutoff valve, if it is closed tightly it may stick closed and may not reopen or the gate disc stem may even break off inside of it... = no water to the house until a major plumbing repair is done. JMO
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