What do these signs mean?
Well not a lot as presented unless you know which country you are in and if that country works in mph or kph (In the order these are in, Canada kph, USA mph, UK mph, France kph)
Similarly if I tell you a colour is RGB 133, 65, 65 you could go on the web or into Photoshop to see what colour that is but you may get different colours or have to answer a question and that question would be which colour space is the colour in?
The colours below are three of the colours that can be represented by 133, 65, 65, there are many more. Left to right they are 133, 65, 65 in sRGB, Adobe RGB and Prophoto RGB.
as you can see they are very different colours even though in their original colour spaces they were all RGB 133, 65, 65. This shows that RGB numbers alone do not control colour, the numbers must be associated with a colour space
The correct terminology for attributing a colour space to a set of RGB numbers is embedding. The embedded colour space tells the software how to interpret the RGB numbers such that the correct colours are displayed. Embedding a colour space in an image is the equivalent of being told the speed limit sign is in kph or mph.