Apologies if this has been asked/answered before, but a search didn't return anything conclusive for me:

My home Outlook client calendar has been sync'd with my Google calendar, and is all loading well on the Galaxy S2. But I've noticed on my calender entries, under the google email address identifying which calendar client it is pulling the event from, there is an alphanumeric code displayed, in the form of D-12 or D-5 etc.

Can anyone explain what this D-number is referring to? It's not part of any editable text fields and isn't something I can attribute to my entries on either home or Google calenders (except perhaps my Outlook categories, but I find no consistency in the values/categories).