I have 14 niche content marketing sites so offline it can become problematic.
What I did was create a domain related to my overall business with a list of all of my sites, a thumbnail image beside each site summary and of course, a link to each site.
Then I had a business card made (I use VistaPrint) and use these cards diligently. I leave them where I visit be it a restaurant, coffee shop, Dr. office, on bulletin boards, absolutely any and everywhere.
I learned to do this years ago in my own brick and mortar business. Leave your card with tips, near the salt & pepper shakers, where you sat in a Starbucks, tucked in a window crease on the bus or train. Be imaginative but every person is a potential visitor to your website(s) and customer.
Of course any meetings, conferences, social gatherings are always opportunities to leave a business card and promote offline. I love when someone asks me, "What do you do for a living?" KaChing! Opportunity is knocking, hand over a business card or two.
BTW: I have magnetic cards and the standard paper variety with information on both sides. Hand over one of each in person.