I'd rather if mk weighed in here, but as far as I know these are because there used to be an ability to vote down on posts which could be used not as intended. If you hover over a share button it has a few fields. (I realised this could be interpreted as "As far as I'm aware a nefarious feature existed that I totally never knew about or used before I mentioned it". It was fun to find out about.)

<a id="down_106576" onclick="return vote(this)" href="http://hubski.com/vote?for=106576&amp;dir=down&amp;b... src="images/img_trans.png" class="2-s-point-h"> </a>

Where the part you're interested in the bit here: http://hubski.com/vote?for=106576&amp;dir=down&amp;b...

In Psuedocode this is vote?=for [Post Number]; dir=[Vote Direction, Up or Down]; by=[Username]; auth=[String that verifies you are who you claim to be];whence=[URL in hex]

Setting dir=down is for unsharing when you've shared it. When you submitted a content form in the past it wasn't checked if you had shared it first, so you could write out the link as dir=down and it would just keep letting you unshare.

For the record, even if you know the auth string it won't let you vote if you're not signed in. I did check, you just get a user mismatch error.