I don’t know if it’s still the case, but in my experience (years ago) PGP messed with the proper rendering of HTTP email bodies.
From a security standpoint also, the signature confirming that the email is from your is a double edged sword: Yes, your contacts get to verify that it’s you, but you’re also losing plausible deniability (privacy).
On the other hand it dilutes the effect of lower values because a lot of them are double digit. 20F, 40F, 60F… all double digit, but wildly varying. On the other hand, with Celsius you get: