Create a trigger by a .sqf script file with the follow code:
_mrk_dim = 200;
_mrk_size_x = _mrk_dim;
_mrk_size_y = _mrk_dim;
_mrk_dir = 0;
_mrk_shape = "ELLIPSE";
_mrk_brush = "FDiagonal";
_mrk_color = "ColorRed";
_mrk_text = "mymarker";
_mrk_type = "Objective";
_mrk_name = "";
_mrk_pos = player; //or your position
_marker = createMarker[_mrk_name,[0,0]];
_marker setMarkerSize [_mrk_size_x, _mrk_size_y];
_marker setMarkerDir _mrk_dir;
_marker setMarkerShape _mrk_shape;
_marker setMarkerBrush _mrk_brush;
_marker setMarkerColor _mrk_color;
_marker setMarkerText _mrk_text;
_marker setMarkerType _mrk_type;
_marker setMarkerPos getMarkerPos _mrk_pos;