Hello Daniele,

I have owned 5 Monzas over the years, including one in NOS condition, a complete package, and the buckle that came on the strap was unsigned, just a plain black one.
Another one of those also came on the same strap and buckle. The same strap yours is on.

Sadly, I lost thousands of pictures while using Windows based machines, years ago, but you can still see that one on the Calibre 11 site.

https://www.calibre11.com/vintage-heuer-monza-series-overview/

Regards