The next few posts are going to focus on Bristol Postage Dues. There are some common causes for covers owing postage due, one of the most common is being posted without a stamp, as shown in the postcard below from Penarth to Bristol in May 1904 which received a large "1d" charge mark.
Another very common cause of postage due is postcards with glitter on the front, which was not allowed and made the postcard liable to the letter rate.
Postcard from abroad that were underfranked, typically with the domestic rather than the international rate, were also common, as in the example below from Canada that was franked on the picture side (more of this later !).
The unfranked domestic postcard below also had glitter on the front so was liable to 2d postage due in 1905.
The international postcard below was unfranked and has a 3d postage due charge. This is a bit of a mystery. As an unfranked international postcard it should have been charged 2d postage due, being deficient of the 1d international postcard rate. There are no obvious reasons why it should be charged at the letter rate (no glitter), and as an unfranked postcard it whould have been charged 5d at the letter rate. The only way one can get a 3d charge that I can see is if it was correctly franked at the international postcard rate (1d) but was liable to pay the letter rate (2½d), giving rise to a 1½d deficiency and thus 3d postage due.
Here is an example of a postcard from the USA that was only franked at the domestic 1c rate and was thus liable to 1d postage due.