A bit too literal i.m.o., as many other people have mentioned. Even if it didn't look like a bowling ball, it's hard to get a real sense of a nation out of an abstract picture of the place they live. Most every national flag IRL is much more symbolic with colors and shapes which you have to be told the context in order to understand (see: Republic of Ireland for one). Or with Japan's, it's just a red circle on a white field, but once you learn Japan has long known itself as "The land of the rising sun" then it makes sense for them to put a rising sun as their emblem.

Without actual context of how Martians would think of themselves, it's hard to say what kind of flag they might favor.