For me, the code in question starts on line 585:
$tmp .= '<a class="gmw-thumbnail-map" href="' . $instance['thumb_link'] . '">';
}
$tmp .= '<img title="' . __('Click to open larger map', 'google-maps-widget') . '" alt="' . __('Click to open larger map', 'google-maps-widget') . '" src="//maps.googleapis.com/maps/api/staticmap?center=' .
urlencode($instance['address']) . '&zoom=' . $instance['thumb_zoom'] .
'&size=' . $instance['thumb_width'] . 'x' . $instance['thumb_height'] . '&maptype=' . $instance['thumb_type'] .
'&sensor=false&scale=1&markers=size:' . $instance['thumb_pin_size'] . '%7Ccolor:' . $instance['thumb_pin_color'] . '%7Clabel:A%7C' .
urlencode($instance['address']) . '&language=' . $lang . '&visual_refresh=' . $instance['thumb_new_colors'] .'">';
if ($instance['thumb_link_type'] == 'lightbox' || $instance['thumb_link_type'] == 'custom') {
$tmp .= '</a>';
I just replaced everything starting at <img title=
and before the closing </a>
tag with the text “MAP”. Works great!