In the old days, if you conducted a search at Yahoo Search, Yahoo would automatically number the results for you. So of the 10 listing, Yahoo would display the rank number on the left of the result.
Here is an example of that in action for a search on google at Yahoo:

Now, the same search, does not display the numbers:

Forum discussion at DigitalPoint Forums.

Comments:
Scott Clark
12/17/2007 06:25 pm
So now it's "Top-ish" rank.
Avromi Sommers
12/20/2007 02:47 pm
You can download the latest version of serp easy surf(Firefox add-on) and it will give you the numbers of the search results in Yahoo. http://serp-easy-surf.seoquake.com/ Thanks to Gleb from SeoQuake for doing this. (It also gives you numbers for Google and MSN)
jsiloman
12/24/2007 07:15 am
Since they stopped numbering, I just use Google . . .
sharonlerose
12/24/2007 07:17 am
serp=easy says it doesn't work for Yahoo. Why the heck would Yahoo do this? I thought they had overtaken Google in popularity . .
stebal4
05/17/2008 11:52 am
You can use the Firefox add-on to show Yahoo numbered results: http://www.bal4.co.uk/2008/05/15/numbered-yahoo-results-firefox-greasemonkey-user-script/