Cleavage from behind

Every year on my birthday I buy underwear.  Ever since my 21st birthday when everyone canceled on my birthday dinner (I know, boo hoo), I have gone out shopping for several hours to buy whatever green and black zebra striped, ruffles on the butt, or boy cut with glitter-flames AND pockets underwear that trips my trigger that day.  But the last couple of years I seem to hit this one store - Princess Tam Tam.  It is on the nicer more modern-retro side despite its ridiculous name.  But for some reason I missed one funny detail until I was running around the apartment half-dressed and packing for a weekend away, my underwear have a cleavage line.

Is that for potential mono-bum?

Really I only made this post because I needed an excuse to show you my underwear.