I've seen lots of SOIC parts that have no painted markings or a dimple on one end on them to denote where pin 1 is.
Look at the plastic body. Look and see if one entire side of it is shaved at a 45 angle.
Typically with parts like this, one side of the chip will be a standard 90 degree, the other at around 45 degree. The side with the angle in it is how you can tell what it is.
Look at the pic below. See the offset in the marking? That's because of the angle in the body. The marking is centered on the flat area. The leftmost pin on the side with the angle is pin 1.