Good info to post mcs1962 since not all people know. Just to clarify though ... this is their policy, not just an offer, meaning it runs 365 24/7 at all Lowe's stores and has been for many years. Note that certain clearance items do not get that 10% discount. They explained it to me a couple years ago and if I am remembering correctly, if the item rings up at clearance price you can get the 10% but if cashier has to enter clearance amount you do not get the 10%. Could be vise versa.
As far as I know, we've never had anything NOT get the discount (even the keyed-in clearance stuff). One cashier said that once and didn't give it to me, but that was HER and not the store. Home Depot also gives mil discount and they are very vet-friendly.
My personal experience is that Lowe's in PA usually honors this 10% however the Lowe's in Arkansas, Georgia, and Virginia limit the 10% to holidays such as Veteran's Day and Memorial Day. PA is the only state that I have lived that honors it 7/365. I recommend checking with the customer service desk before you fill up the shopping cart.
UPDATE: I went to the Lowes and Home Depot in Pennsylvania and Virginia over the past two weeks and they really screened my ID. The cashiers stated that only active duty Soldiers are authorized the discount. In the past Reserve and National Guard Soldiers received the discount but civilians working for the military (GS employees) were also using their military ID to get the discount therefore they are only giving the discount to active duty Soldiers.