[Alaska Wolf]

Yes, I have, many times

Then it should be quite easy for you to post one that states, "Driving 110MPH is disallowed". Thank you in advance.

Why are there speed limit signs and who has the authority to post them?

[JustSayNoToNannies]

I've never ever seen a speed limit sign stating that driving 110 mph is disallowed, have you?

Yes, I have, many times, [TEXT OMITTED BY ALASKA WOLF: since "speed limit X" means driving at any speed faster than X is disallowed.]

Then it should be quite easy for you to post one that states, "Driving 110MPH is disallowed".

That's not the question you asked - I answered the question you asked in the text you omitted from your response. Since it's not practical to list every speed that is disallowed under a speed limit regulation, that's not how speed limit signs are worded.

Why are there speed limit signs

To inform drivers as to what the speed limit is.

and who has the authority to post them?

In Minnesota it's "local road authorities" - not sure exactly who those are ... cities' and townships' Departments of Public Works, maybe. Why do you ask?