Your button is a variety of US Navy buttons shown in the Albert button-book as NA-75A and 75B. Apparently, they were manufactured to fill an order from the Navy, but the order got cancelled, perhaps because the design of US Navy's logo on it got changed significantly (to having the eagle stand on an anchor). So the manufacturer, who is unknown, converted the unsold buttons for Civilian use, by putting the thread loop on the Logo side of the button.
Time-dating your button:
We know that the US Navy button with the anchor inside a spade-shaped shield came after the 1812-era version with an oval shield. We also know that the eagle-standing-on-anchor version first appears "about" 1820. So, the timing of the emblem changeover tells us when your "converted US Navy leftover" button was made.