Road numbers' colors/shapes in Google Maps

I would like to expand on hippie's excellent answer with respect to Saudi Arabia. The highways symbols with the country map outline are national highways, which is a recent development as Saudi Arabia continues to build out its road infrastructure.

In Saudi, the older signs simply had the name of the major destination, and the road was named for the major cities along its route. This is a sign on the Dhahran-Khobar highway:

Later on, the cross-country roads were numbered in a state highway system; these signs now have the road number and if it has the Saudi country outline, its a national highway. In this image, you see Makkah (40 West), Qassim (65 N) and Kharj (65 S).

Saudi state highway 40 runs from Makkah (on the west coast) to Dammam (on the east coast); it is one of the most used national highways in Saudi Arabia, as it passes through Riyadh (the capital).

As you can see, the signs are in English and Arabic, but the road symbols are in Arabic numerals with the direction in English and Arabic.

In addition to the above, there are other road symbols as well. For example, this sign displays a couple of them:

From the top left, there is:

1. 40 W (main highway leading to Makkah)
2. The road symbol for the Holy Mosque (this is shown when roads lead to Makkah and within Makkah to the Holy Mosque). These were added as a universal pictogram (similar to the airplane outline that identifies an airport).
3. The white sign with 80 M is the local motorway designation.
4. The symbol after it 267 is the regional road marker (a local road that is off the main highway). In this case, it leads to the mountain city of Taif).