How would you call a stele on the road at the city entry like this?

This is a Welcome (city) sign, as stated in Wikipedia Wiki:
- A welcome sign (or gateway sign) is a road sign at the border of a region that introduces or welcomes visitors to the region.1 Examples of welcome signs can be found near political borders, such as when entering a state, province, county, city, or town, and they are increasingly found in neighborhoods and private communities.
The Welcome to Fabulous Las Vegas sign:
- is a Las Vegas landmark funded in May 1959 and erected soon after by Western Neon. The sign was designed by Betty Willis at the request of Ted Rogich, a local salesman, who sold it to Clark County, Nevada.

(Wikipedia)
These are generically called Monument signs
Here's a Google image search for "monument signs"
And I would refer to a Monument sign at the border of a city to be a city monument sign