HSBC Premier Mastercard holders are eligible for 15% off hotels bookings made on Expedia as well as an instant Expedia+ Gold status which gives you a 30% points bonus on all Expedia Rewards base points as well as an addtional 250 bonus points for +VIP Access hotel stays. Typically, one can hit Expedia+ Gold by booking either 15 room nights a calendar year or by spending S$10,000.
The Expedia+ Gold Status will be valid for 12 months from the date of registration and it seems like only the first six digits of the card are required for this purpose. I already have Expedia+ Gold (since I book a lot of my flights on Expedia) so I will not be able to try it but it seems like anyone can sign-up for this (even though they should not!). Saving 15% off hotel reservations is quite a nice perk but it is important to remember that most credit cards in Singapore offer you the opportunity to save 10% on bookings (you can typically stack this with ShopBack to get maximum value even though according to the terms and conditions it should not work).
In order to get 15% off an eligible hotel stay, you will have to enter 'HSBCMASTERCARD15' as a promo code and payment needs to be made using an HSBC Premier Mastercard. In case you are wondering how can you actually get your hands on this card, it is exclusively for customers who have an Premier relationship with HSBC - you may wish to check out my previous guide on Priority Banking in Singapore for a quick comparison of the different AUM requirements across banks.