From v9.7.3, a map icon has the option to draw a stripe of solid colour at the right edge of the note. The edge coloured is only ever at right and not subject to user choice.
$Stripe determines the width of the stripe, in pixels at standard scale; if $Stripe has no value (the default) no stripe is drawn.
The colour of the stripe defaults to $AccentColor, but may be set to any colour by changing $StripeColor.