If one randomly chooses a standard coin in circulation anywhere in the world, and flips it, what is the probability that it lands heads?

(Note: I actually don't know the answer to this question, which makes it a bit interesting: how many coins actually have heads? Maybe there are coins with heads on both sides?)

Resolves to MKT, meaning resolves to whatever the market probability is at the time of close.

The market close will be a date chosen uniformly at random between 9/24 and 9/26 (inclusive), to help avoid issues with last-minute trading. Here is a possible procedure I may use (subject to change): On each day, I will generate a random integer between 1 and the number of days remaining, and if the generated number is 1 then I will close the market. The time I perform this procedure on each day will be arbitrary, and I will not perform any trading immediately before or after carrying out this procedure.

: There are many ambiguous, hard-to-resolve questions that people have created on Manifold that use a "self-resolving" mechanism of resolving to the market probability. However, there are many concerns about how well such mechanisms work and how reliable they are especially against price manipulation.

This experiment is similar to other recent experiments, but with the answer expected to be close to 50% instead of close to 100% or 0%. The hypothesis I wish to test is whether that makes a big difference to the accuracy of the market. 

Some examples of other markets using self-resolution are in the group 

https://manifold.markets/group/selfresolving

What is the probability that a coin flip lands heads? [Resolves to MKT]

 → What is the probability that flipping a random coin anywhere in the world lands heads? [Resolves to MKT]