You can read about my full rationale here, but essentially (shills aside) we all believe in UASF – if we coordinate our efforts and pick one major wallet/exchange per day and bombard them with demands to support BIP148, we can make a real impact. And today I think we should target Coinbase.
Here, I've made it easy for you:
Post on their subreddit. (Honestly, I was kind of surprised this is a thing too)
Ideally do all the above.
Let them know you support BIP148 and segwit. Let them know their users risk losing all their bitcoins if they do not. If you are a customer, let them know that you will withdraw all your funds unless they commit to supporting BIP148. Be polite, but firm.
I believe it is time for BIP148 and I believe we the users have a vital role to put pressure on major exhanges and wallets to demand they commit to support BIP148 chain from August 1.
Because Bitcoin belongs to the users.