Here are a few PPB registration labels. PPB stands for pejabat pos bergerak which is Malay for mobile post office. This abbreviation was used after North Borneo/Sabah became part of Malaysia. I find it rather confusing as to why the postmarks used on these covers were not the PPB type.
This "modern" stuff is by no means easy to find.
Update I have information that these label may have been remainders used due to lack of the normal labels or the practical decision to use up surplus. Therefore these covers are probably not PPB type. Anyway, the labels are shown quite nicely.
This Tenom PPB is probably not that common. Again the postmark is not the PPB type. There are at least 3 types including a hand stamp cachet.
This Kudat PPB1 label is again not recorded in the journal. It is one of at least 6 types including one cachet.
This is a nice Kota Kinabalu (Jesselton) MPO 1 label. KK had labels for MPO, PPB and also railway TPO. You can see the misnomer Kudat MTO6 and the KK PPB1 by clicking here.