Cragle, a contributor to the main two Zodiac Killer forums, brought my attention to two sections of the Volkswagen Karmann Ghia door of Bryan Hartnell where there appears to be additional writing. The cardboard obscuring the car door on the right side is noticeably larger than the cardboard taped to the left side. This would have little significance, if it were not for the apparent lettering that seems to be present - particularly on the bottom right side where the two letters of M and L (or something like them) are just visible.
We know that the "by knife" phrase was initially withheld from the newspapers, to distinguish between the real killer and any hoaxers, had the perpetrator of the stabbings at Lake Berryessa made contact with the police. In the San Francisco Chronicle article published on October 1st 1969, the investigators stated "there were a couple of other things we're still holding back so we'll be able to identify the man if he wants to call us again". We know that the "by knife" phrase was one, so could this potential hidden writing be the second.
Of course, there are subsequent images of the car door that show its right side without any writing, so these images would have required doctoring to conceal any writing on the right side and keep the message (if one exists) under wraps.
Of course, there are subsequent images of the car door that show its right side without any writing, so these images would have required doctoring to conceal any writing on the right side and keep the message (if one exists) under wraps.