What a great hunt in the yard tonight, found my first ever indian head penny 1905 also my oldest coin so far. A military button, not sure how old. Last but not least the WMD a Callen Cap Grenade, looks like a little bomb. HH to all.
Your military button is a US Army "Great Seal" button. The army first started using the "Great Seal Of The United States" on its uniform buttons in 1902. But because yours has a raised rim AND what is called "black finish" on its front, it dates from the World War One era to 1923.
I cannot tell you guys how excited I will be if I EVER find anything really cool (uniform button, bullet, plate) that I know I won't be able to identify and have TheCannonBall guy set me right. I'm amazed at his vast knowledge and applaud his willingness to share the wealth.