duckfiasco wrote:I've read two seemingly conflicting things on this stage. First, that a "sign of concentration" will appear, such as some visual phenomenon of a sun or cloud, but conversely I've read that the sign is actually a physical sensation of pleasure.
There are various potential signs including both of the above. No classical instruction text (e.g. Śrāvakabhūmi, Visuddhimagga, etc.) limits the sign of mental calm (śamatha) to any single phenomenon, but all do emphasize and single out bodily and mental pliancy, as well as joy and pleasure as necessary requisites.
duckfiasco wrote:Basically, I'm not sure how to tell when you've developed access concentration. And then when to pick a pleasant physical sensation to concentrate on, or if that's wrong altogether and I should wait for some clear "sign" to appear that I'll know when I see.
It's usually best to follow the instructions of one teacher or one practice system/tradition and stick with that. In this respect, face to face communication with an experienced teacher is quite helpful for addressing your specific questions and making appropriate adjustments when necessary. If this isn't possible at present, then IMO it's prudent to just stick with the main object-support, such as the breath, and not worry too much about signs of progress. Eventually these will become obvious.