I came across an regulator IC/Chip from ST microelectronics MC34063A(SO-8 package) which didn't have any kind of standard pin no 1 marking on it. My work got held up because i was not able to proceed with the soldering and assembling of the board.
I did write to ST microelectronics support engineers, but for no avail. I did not receive any reply from them. We had ordered the part from Digikey. The datasheet showed that the pin no 1 for the SO-8 package will be identified by half circle notch but, the part i had ordered didn't have any kind of marking(notch,dot,line,bevel) except the name of the IC. Strange..!. After a lot of googling i found a discussion on a same kind of IC which didnt have pin no 1 marking on it. There they had mentioned that the pin no 1 for such parts is identified as follows,
"If the IC/Chip has got no markings then hold it horizontally so that the writing is from left to right and now the pin no 1 is the one on the bottom left."
Its 100% correct..! The IC worked after soldering this way..!
Here are a few images which might help you in identifying the pin no 1 in a chip/integrated circuit.
The image shown below is applicable for two sided chips like DIP,SIP,SO,SOIC
The images shown below are for SIP packages..
Normally you should not have any problem finding the pin no 1 on any IC as it's datasheet should have the information about how the pin no 1 is marked. So, first refer your datasheet. :)