If you want to be sure you have them you need to crafty. When you have been in bed a few hours and can sense them, very quickly turn the sheets back and the light on. You will see them on your sheet. particularly if they are plain sheets.
You may also see "blood spots" on your sheets and pillows - their faeces.
If the infestation is very bad, you can smell them - a strange odour.
I was in Singapore in the early 70s and a place I stayed in had them, as Ethel says, you'll have bites all over, and you'll also be scratching like billio.