Furthermore, speech accompanying a cryptocurrency transaction would be something courts call "commercial speech" -- speech that "proposes a commercial transaction or relates solely to the speaker’s and the audience’s economic interests" [0] -- which is an established exception to the First Amendment. It's not unprotected from regulation; but it does get a reduced level of protection when there's a legitimate government interest on the other side of the balance. See this explainer from the CRS:
[0] https://crsreports.congress.gov/product/pdf/IF/IF11072 ("First Amendment: Categories of Speech")