"Jest" isn't always the accurate way of putting it because it's not always "joke" as such; "I didn't literally mean what I said here" would indeed be a better way of putting it. However, as that sounds unutterably lame I tend not to go for that.
And Jack: trust me, the smiley route doesn't usually work for me, I know that from historical evidence.
Either way, I'll try - again
- to convey more often when I'm not being 100% serious in a post.