Nether Portal Activation Hint

The natural spawning nether portals in the overworld lets players figure out what a nether portal is without having to use external resources. This is good but what is missing is clear hints of how to active the portals. My suggestion is that sometimes, the obsidian blocks on the bottom of the portal sometimes catch on fire and after some time (short time) a 1x1 portal block spawns on the obsidian block which was on fire and then the portal block quickly disappears. This would indicate that fire spawns the portal block (indicating how to activate a portal).

An alternative to this is could be giving crying obsidian an unique behaviour which spawns fire on top of itself so that the bottom portal blocks (that may or may not be crying obsidian) spawns a fire which then spawns a temporary portal block.

Or, obsidian blocks (or crying obsidian) could attract lightning which then creates a fire which consequently leads to the portal block effect.

To avoid exploiting this there could be a cooldown time of x seconds (enough time so a player can't use that single portal block to go to the nether) before that portal block could spawn again.