The dots are vent holes, intended to vent air and gasses as the bottle is blown, allowing the glass to better fill all the embossing for crisp lettering and details.
When the mold/lettering becomes very worn, the situation you see here develops, the vent holes become more pronounced, forming dots, and the letters recede or fade.
Over the years I have seen a few where the letters can hardly be read at all, and the vent holes almost look like braille.
