Traditionally, with 'wet' signatures (using a pen and paper) the purpose of adding initials was to show that the signer is "approving" or accepting the terms of a particular page or clause. The use of initials is not required anymore with digital signing. With SignRequest, all electronically signed documents are tracked back to the signer via the Signing Log.
Alternatively, rather than adding initials, you can simply add a checkbox field so the signer only needs to check a box, indicating that they approve. This input will be linked to the specific person via the Signing Log (shown below).
The Signing Log validates this "check mark", so it can be deemed to be just as valid and binding as an electronic "initial".
If your specific workflow still requires the use of initials, SignRequest offers the "text" field, which can be used to request or add initials.
You can add a description, to indicate to the signer that an initial is what's being requested.
The signer can simply type their initials into the text field.