New discovery! Original photo used for parking_meter02 texture.

[Bruner]

Found this yesterday while looking for more photos that could be added to the Real World Prototypes art gallery on the website. I knew I wasn't easily gonna find a similar parking meter by just searching "parking meter" on Google, so instead I tried "Seattle Washington parking meter" since Seattle is where Valve is located, and they've probably modeled a lot of assets off of things in Seattle.
By sheer dumb flippin' luck, one of the first dozen of images that shows up is the exact photo that Valve used for parking_meter02.