There is no meta-gaming.
Consider: The GM can tell the players, "As you walk outside, you see the sun bright in the sky. It's a lovely day!" It's not metagaming for the players to act on that information - eg to choose to leave their rain cloaks behind, so as to avoid encumbrance from them.
Likewise, if the fiction is apposite - eg a character educated in runic matters looking at a runic circle - then the GM can tell the player of that character, "You see a runic circle. It looks to you like a symbol of protection." Or even, "You see a runic circle. You recognise it as a runic circle."
When it might be appropriate for the GM to say such a thing depends upon various considerations, including some that vary from system to system. I take up some of these matters below.
Why not?
In my Torchbearer 2e game, two of the PCs started with significant Lore Master skill. In my Burning Wheel game, it's pretty common for wizardly PCs to start with Aura Reading and/or Symbology. In 4e D&D it is mandatory for wizards to start with Arcana skill.
There is no reason to think that a runic circle would be especially mysterious to these PCs.
In each of these games, a runic circle is something the GM might introduce into a scene, and mention to the players. The principles by which the GM might then dispense information about it is varied. Suppose a player asks "What do the runes say?" the GM can simply reply (in 4e D&D and BW, this is "saying 'yes'"; in Torchbearer this would be rewarding a "good idea", of reading the runes). Or can call for a check, if something is at stake in whether or not the PC recognises the symbols.
But this is all about game play. There is no premise that PCs educated in the magical arts will, in general, be ignorant of runes.
And what a skill check represents can vary across and within these games. BW can be particularly subtle in this respect, because of the way its rules for combining skills into a single check work. There is no reason
in general to think that a check represents a character acquiring new knowledge, or cudgelling their wits. On the other hand, in 4e D&D an Arcana check may well represent the acquiring of new knowledge (by "identifying" the magic), and the same is true of Aura Reading in BW.
Whether or not there is a mystery here is entirely in the control of the GM. There are any number of other possible mysteries in the neighbourhood, too, such as - Who inscribed the runic circle? Why here? What were they seeking protection from? Or what were they seeking to protect? Etc, etc.
There is nothing inherently
more exciting about learning the nature of the circle than learning any of these other things, and for my part I incline to agree with
@hawkeyefan that learning the nature of the circle is towards the bottom in this respect, because in itself it does not tend to propel play forward as these other things might tend to.
This is a very prescriptive account of how to GM a RPG, even for D&D. It's not one that appeals to me either as GM or as player. There are many reasons why this is so, but one of them is the suggestion that all interesting information should be gated behind low-stakes skill checks.
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