My question is, do you know where we could advertise this type of sale?

Go to Etsy and search for "rental property tracker," and you will find hundreds of nice spreadsheets to track 10-20 rentals, usually for under $10.Software has extremely helpful features like online payments, marketing syndication (click a button, and your property is advertised on multiple sites), electronic document review/signing, maintenance tracking, and owner reports.

Not only for the element of surprise, but also for the comfort of everyone around you and not advertising the availability of a weapon to anyone who might want that weapon.

Why not just advertise it as W/D available upon request?

Most postal carriers have enough common sense to recognize which box is for unit A and which is for unit B.

Best to do this properly and ignore the people who say not to advertise this. 

Recently acquired duplex and used Avail for everything- advertising, screening, lease signings, deposit collections, etc.

They reached out to me to pay $3500 for a SFH for a short term rental when the advertised rent was $2500 and I only wanted long term renters.

CS is just a difference in the timing of when depreciation is recognized (or what is depreciated), it shouldn't change the nature of the investment type (short term vs long term).

Soon after purchase, I started advertising the space for lease and we received overwhelming interest.