Check if a point is inside polygon in OpenLayers 3

You have a method 'intersectsCoordinate' for the ol.geom.Geometry.

So the code for that will look like:

var polygonGeometry = e.feature.getGeometry();
var coords = iconFeature.getGeometry().getCoordinates();
polygonGeometry.intersectsCoordinate(coords)

You can use the JSTS library, which implements simple geometry processing such as intersects, difference, etc. It contains an OL3 parser that allows the conversion of geometry from OL3 to JSTS and vice-versa.

See an example in OL3. Basically, you would use a process that checks if the geometry of your marker is within your polygon or not and do what you want from there.