It's really cool today. What symbol do you use?

Use exclamation points. It's really cool today. This sentence is an exclamation. Punctuation marks need exclamation marks to express the speaker's strong feelings about good weather, so use exclamation marks.

Exclamation mark is a kind of punctuation mark, also called exclamation mark and exclamation mark. Used at the end of a sentence to express surprise, mainly at the end of an exclamatory sentence to express strong feelings.