At the start of any book with the OSR Compatible logo (we still need one), there should be a box with a description of the stat block. For D&D type games, I see this looking something like what follows:
This module is OSR Compatible, and will work with most old school fantasy RPGs and their modern clones. It was designed with the classic game in mind but can be adapted for your game of choice.The important notes to hit will be:
Encounters are listed in the following format:
Orcs (4) - AC 6 (13), HD 1, #AT 1, D 1d6
Armor Class is given both descending and ascending values. An unarmored character is AC 9 (10) and chainmail gives AC 5 (14).
Unless specified, all encountered creatures and men are assumed to have the same movement rates as normal men and to use the same saving throws as a fighter of the same level as their hit dice.
- The boilerplate indicating compatibility. I think talking about "original," "advanced" and "classic" games will let us indicate compatibility in a broad and understandable way without stepping on any toes.
- Encounter format. A basic stat block for illustrative purposes.
- Armor class. This should always be described and an unarmored character's AC given, along with an example of one armor type (typically leather, chain or plate).
- If you choose not to include movement rates, armor class, hit dice, or damage, give a brief description of your default values. For instance, if all creatures are assumed to attack once per round for 1d6 damage, say so.
- If you use any stats other than the basics, present a brief description and what value is better. For instance, Moldvay-style morale would be described as: "Morale is given as a number between 2 and 12. Creatures with a high morale are less likely to flee from combat."
To be clear - this is a self-designation, not a license, and I'd want to have the logo be licensed via Creative Commons CC-BY (by attribution, allowing it to be used in derivative works without requiring that the larger work be released as a CC license).
How does this strike people? I think it's going to be easier to build consensus around a flexible standard than to come down with a list of things that someone has to use, and it's best to be up front about exactly what parameters we're using so that it's as easy as possible to convert.