To be honest, a Leica is much more discrete than a Bentley. If you don't like the Red Dot branding, you can cover that up with a piece of black gaffer tape. But a Leica or other small rangefinder cameras (eg old Contax, Zeiss, Voigtlander) are the epitome of the stealth camera - small, unobtrusive, quiet and definitely not flash. You can even put it into your jacket pocket. The complete opposite of a SLR or larger modern mirrorless camera with large lenses.
I accept that Leica prices are steep, very steep. But if you are an old film camera user, you could pick up a M10 and use it without even looking at a manual. You have a shutter speed dial, a film speed/ISO dial, manual focusing and an old fashioned aperture ring on the lens. You don't have to reach for the manual to look at the menus to change the ISO or change the shutter speed/aperture. Everything falls into place, just as you'd expect it to.
My suggestion would be an used M10 - great image quality, quiet (virtually silent shutter - pretty much as quiet as the M2 and M6) with a small 35 mm lens (vintage Leica or new Voigtlander 35/1.4 Classic). If you already have a M2, you could just use your existing Leica lenses.