SEA LAND CONTAINERSHIP SERVICE 1973 1974 WATCH CALENDAR HONG KONG ADVERTISING For Sale

Vintage 1973 1974 SEA-Land Containership Service Calendar. You are supposed to attach this metal piece to your watch band so you have a calendar handy. Vintage Advertising item. The case has a missing tab on the hinge...see the pics. Otherwise looks good. Very unique advertising item from the early 70s. My mom worked for Sea-Land so I assume she got this there. Have never seen anything like this before....wondering if people actually attached these to their watch wristband??
Niche Collectibility: Sea-Land is highly historic (founded by Malcom McLean, the father of containerization). These aluminum tabs were popular corporate promotional giveaways in the 1960s and 1970s. Users would bend the small side prongs around their watch strap to add a calendar function to a standard watch.