For me these are items that will get occasional wear (not everyday wear) but which I will keep in the long term. I have quite a few because I’m trying to use this as a strategy to collect nice/high happiness factor things in my wardrobe that I can pull out again and again and not tire of. I may not keep them forever, but I’m aiming for 10 years plus. For that to work they must have qualities that I have consistently gravitated to over the years. And not be a recent trend, unless that trend happens to coincide with a longstanding love affair. If I buy something trendy that is more a recent interest, like a tiered skirt, I want it to be an everyday wear item so that I can wear it a lot before the trend changes.
Characteristics that tend to make something iconic for me are:
Favourite silhouette (long slouchy pants, asymmetric longish skirt, high neck top)
Favourite colour (teal, dark green, burgundy, muted metallic)
Favourite fabric (silk, brocade, leather, wool, velvet)
Favourite pattern (dark floral, tie dye, ombre, marble print, geometrics, quatrefoil, abstract analogous colour print)
“The vibe”: sophisticated, modest, unique, interesting, luxe, moody, classy (all from my personal perspective of course)
They are usually a bit statement-ish.
A lot of my icons are cool weather items, which is another reason why I use this strategy because our winter is short and I want to choose items that will stand the test of time. For summer, I can afford to be a little less picky because our Summer is long and intense and items get worn more and worn out faster.