] Ensign: An ensign was the lowest grade of commissioned officer in an infantry regiment.

So Wickham would be starting over again from the bottom. (Not that I think he had attained a much higher rank in the militia!). Now that I come to think of it, why is his rank never mentioned througout P&P? We have Colonel Forster, Captain Carter, and just plain Denny, but Wickham is "Mister" Wickham. Was it because officers below a certain level were addressed as "Mister", not by their rank? Does anybody know?