I think Les has the most likely interpretation, given the rather upbeat nature of the song...

Just to further confuse the issue, here's a quote from Dylan's "Absolutely Sweet Marie":

Now six white horses that you did promise
Were finally delivered down to the penitentiary
But to live outside the law you must be honest
I know you always say that you agree
But now where are you tonight, Sweet Marie?

Someone'll probably say it's about heroin. I doubt it. I think it's just one of those symbols Dylan instinctively dredged up out of his incredible backlog of trad material. The 4rth and 5th lines are the really interesting part of the verse anyway.

- LH