The Minolta "Secret Handshake" (or even Minolta Handshake) is the honorary name for the epic Minolta Maxxum 28-135mm f4-4.5.
This is one of my favorite outdoor zoom lenses. In my opinion the wide-end is adequate on APS (5D/7D, A100-A700 and newer) and 135mm fantastic. The range is superb on a full frame camera body (A850/900) of course. The unique rear focus mechanism is surprisingly fast for a lens of its age. Image quality in virtually every respect is difficult to match, although some may criticize its lack of contrast compared to modern lenses.
It is the "secret handshake" because it is not well known but those few who do know it, understand the secret. It is easily overlooked because it doesn't stack up well on specs and given its scarcity, not many people to talk up its virtues. On camera forums people say, "Well it isn't very fast and it isn't very wide, so I don't know..." It just doesn't feel like it will be a lens that will be useful in enough situations, so people skip it.
I understand, I was once the same way and I think my Tamron 17-50/2.8 is great... but seriously - if you had to pick one lens - or even one anything to live with for the rest of your life, wouldn't you pick something with shortcomings that you love over something that has all the right features but leaves you a little cold?
Sure, sure I am going over the top here, but I hope this serves to explain the idea of the "secret handshake." If you fall in love with this lens it is so worth it. If you don't if will keep its resale value forever, so really there is so little risk there. The great Minolta classics are one of the great strengths of the
Minolta Sony A-mount, take advantage of that.
You can read more about the Minolta 28-135/4-4.5 on its dedicated page.