[postalbyke]

I know "on the boat" (US Navy) our systems have built-in symbols, but nothing built in to notify you what they're for, each ship has freedom to assign them at will. For us it was squares for merchies (convenient) (yellow unknown, blue friendly, red enemy) diamonds for "surface combatants," bottom half circles for unidentified subs (not really used) bottom half diamonds for submerged contacts (every sub is an enemy sub lol) top half stuff for aircraft, circles for special case surface contacts.
That's all in the computer tracking software.
On the charts it's all lines and dots, x's, whatever they've got around for markings. Ownship is only a circle to indicate position of uncertainty: "we're in this circle (we hope)."