I recently posted the following in a puzzle thread
Finally may I remind people of one of the points in my Advice for Newbies and Regulars 'Sticky'.
"Ruud’s Weekly Assassins have their solutions posted in the Archive. If you are the first to post a walkthrough for a forum puzzle it is a good idea to give the solution at the end of your walkthrough so that others can check their solutions. There is no need to do this when the puzzle is a variant of the original Assassin which has the same solution."
If the first walkthrough is posted in "cloaked" text, please add the solution separately at the end in tiny text. Then it will be obvious that a solution has been posted without looking at the "cloaked" text.
A better alternative has been suggested to me.
All puzzle creators, starting from now, are requested to post the puzzle solution in tiny text after the code string for the puzzle. For example
Solution:
654921873
371548296
928376451
245689317
716253984
893417625
432195768
589764132
167832549
The solution should remain in TT so that any Newbies coming across the puzzle, maybe weeks or months after it was first posted, will know that there is a solution but not read it accidentally.
If the puzzle creator doesn't post the solution, then the first person to post a full WT should also include the solution.
Many thanks for a great suggestion, Afmob!