Before the widespread use of telephones, before cellphones and pagers, before email, Facebook, Twitter, Snapchat, Skype, and Yo ... there were postcards.
It was probably a little embarrassing to let postal workers and anyone else who was in a position to glance at your mail know that you were lonesome. But the only viable alternative was writing a private letter and putting it inside an envelope. Perhaps the public nature of this postcard was the whole point. If you sent one to Charlotte in Dubuque, her parents, siblings and mailman1 would all know that you were lonesome and that Charlotte was your target.
This card was never used. As you can see, no city or address or meeting place has been written within the green pennant. The reverse side of the split-back postcard was never written on. The only identifying information is "No. 628 — Lovers' Pennants — 32 Des."
So it could still be deployed for its original purpose. At least you would know that it wouldn't get lost in a spam filter or be subject to a cellphone dead zone.