It may be helpful to post a pic of that coin to get an accurate answer. That always helps when you're asking a question about a coins design or details. The only obvious answer I can give you without seeing the coin is grease may have clogged that part of the die and therefore obliterated the designers initials from the coin. Post a pic if you can. BTW, Welcome to the forum!!!
I've seen many, including on proof walkers. I may be wrong about this, but I believe they are not worth much of a premium, and can often be caused by grease filled dies as previously mentioned.
Welcome to the forum budbrain. The Cherrypickers Guide lists a 1945 walker with the missing designer's initials and the variety is more valueble for the 1945's walkers. So your 1929 - S could be worth more than a regular 1929 -S walker due to the missing designer's initials. Lou
If you check out Breen's book he says for the 1929-S No AW..."Presently very rare. From dies drastically relapped after clashing. About 15 reported to date, mostly in low grades." This source is from 1988...who knows what the satus is now. Larry Nienaber
Read the post above---Breen was great at making up numbers for how many where reported. The value of this error is just alittle over what the coin is worth. If you can post a photo of the coin maybe we can be of more help with the value. Speedy
The initials are raised on the die and incuse in the coin. Intentional die abrasion ("die polishing") will remove the initials before anything else.