This is how the referral codes work: An item has a code added to its URL to indicate where it appears. In the case of the front page treasury items, they will have a referral code of fp_feat_1 through fp_feat_12 attached to the URL for each item, with the number indicating the position. Position 1 is the upper left, and they number left to right up to position 12 in the lower right.
A "normal" item URL looks like this:
An item URL with the referral code for the item in the first position on the front page looks like this:
These location codes are added to the URL in several places around the site, such as the search results and the showcases. They seem to have the purpose to tell Etsy (and maybe, someday, the sellers?) where the traffic to an item comes from within the site. Sounds like a good idea right?
But there's a potential downside. First of all, as far as the internets outside Etsy is concerned, the "normal" URL and the appended URL are different locations. Why does this matter? Well one reason it might is that Google and other search engines rank pages based partly on how many other sites link to them. Let's say two different bloggers copy and paste a link to one of your items, but one of them finds you through a search and the other finds you by browsing the categories. The links they copy will have different referral codes inserted in them. Google seems to treat them like two different pages Take a look at the Google results for this Etsy item:
Look at the URL in green. Google has indexed this single item as four similar but separate pages. The top result is one that links from a search in gallery view. The "normal" link is next, the third one is also from a gallery view search and the fourth one from a third-level category browsing page. All have the same item number, all link to the same item. Google keeps its ranking system a secret, but it appears as though giving one item several different URLs may divide up its traffic in Google's eyes, potentially reducing an item's ranking in search results. Maybe someone with more SEO savvy can weigh in on this?
Anyway, for your edification, here are some of the location codes you may see in item URLs on Etsy:
|sr_list_1 through sr_list_21||Search results in list mode|
|sr_gallery_1 through sr_list_21||Search results in gallery mode|
|fp_feat_1 through fp_feat_12||Front page treasury items|
|fp_gg_0 through fp_gg_100+||Front page gift guide items (upper left scrolling window)|
|fp_feat_13||Front page - three items from the featured seller's shop|
|sc_main_0 through sc_main_49||Main showcase|
|sc_storque_main_0 through sc_storque_49||Storque showcase and so on, using the showcase title (sc_children, sc_candles, etc.)|
|em||"Related items" in Storque articles|
|cat1_gallery_1 through cat1_gallery_21||Top level category page gallery view|
|cat1_list_1 through cat1_list_21||Top level category page list view|
|cat2_galley_1 through cat2_galley_21||Second level category page gallery view (note the typo)|
|cat2_list_1 through cat2_list_21||Second level category page list view|
|cat3_gallery_1 through cat3_gallery_21||Third level category page gallery view|
|cat3_list_1 through cat3_list_21||Third level category page list view|