[Dignity]

pawn Code:

// Credits to AbyssMorgan
stock Float:GetDistanceBetweenPoints3D(Float:x1,Float:y1,Float:z1,Float:x2,Float:y2,Float:z2){
    return VectorSize(x1-x2,y1-y2,z1-z2);
}  

PreventMapIconStack() {

    // For the loop
    new MAX_MAP_ICONS = 1024 ;

    // distance you want to stop the stack in
    new Float: MAX_MAPICON_DIST = 25.0 ;

    // Mapicon type /model you want to check for
    new LIMIT_MODEL_ID = 31 ;

    // ID to store last visible map icon in
    new LAST_EXCEPTION = -1 ;

    // Two sets of coord variables so we can check distance
    new Float: x1, Float: y1, Float: z1 ;
    new Float: x2, Float: y2, Float: z2 ;

    for(new i; i < MAX_MAP_ICONS; i ++){

        // If our type / model isn't the one we want, continue the loop / skip
        if(Streamer_GetIntData(STREAMER_TYPE_MAP_ICON, i, E_STREAMER_TYPE) == LIMIT_MODEL_ID){

            // If last_exception isn't set, let's go ahead and set it
            if(LAST_EXCEPTION != -1){

                if(IsValidDynamicMapIcon(LAST_EXCEPTION)) {

                    // Let's get our coordinates so we can check distance
                    Streamer_GetFloatData(STREAMER_TYPE_MAP_ICON, i, E_STREAMER_X, x1);
                    Streamer_GetFloatData(STREAMER_TYPE_MAP_ICON, i, E_STREAMER_Y, y1);
                    Streamer_GetFloatData(STREAMER_TYPE_MAP_ICON, i, E_STREAMER_Z, z1);

                    Streamer_GetFloatData(STREAMER_TYPE_MAP_ICON, LAST_EXCEPTION, E_STREAMER_X, x2);
                    Streamer_GetFloatData(STREAMER_TYPE_MAP_ICON, LAST_EXCEPTION, E_STREAMER_Y, y2);
                    Streamer_GetFloatData(STREAMER_TYPE_MAP_ICON, LAST_EXCEPTION, E_STREAMER_Z, z2);

                    // Checking distance...
                    if(GetDistanceBetweenPoints3D(x1, y1, z1, x2, y2, z2) < MAX_MAPICON_DIST){

                        // Set the "playerid" to MAX_PLAYERS+1 aka nobody so nobody will see the map icon
                        Streamer_SetIntData(STREAMER_TYPE_MAP_ICON, i, E_STREAMER_PLAYER_ID, MAX_PLAYERS + 1);
                    }

                    else continue ;
                }

                else LAST_EXCEPTION = i ;
            }

            else LAST_EXCEPTION = i ;
        }

        else continue ;
    }

    // Re-stream the map icons if need be

    return true ;
}

Untested, but something like this is what you need.

edit: Added some comments / pointers