Categorize emails for Subscription Center preferences

Hi all,

We are looking to set up email preference center and want to be able manage subsriptions/unsubscribes for the marketing emails/newsletters/cross promotion emails. 

Can someone shed some light on how we can categorize these emails in Marketo? Should we create folders while we are working with these email types to be able to categorize them and know what type of emails that belongs to - is it a newsletter or marketing email or cross promotion? 

At this point we do not have these categories andwe have no way to tell what kind of email it is till we open them.

Please let me know what are the various ways of tagging these emails.

Thanks!
Khushboo