Well, good job on finding Cicada Mark #1! they are all pictographic pointers to the next clue. The brooch is the toughest to find, and leads to a mysterious man with a quest that isn't finished yet (one of the "to be continued" ones).

If you still want a full detailed description on the steps to complete, I'll tell, but it would be a total spoiler :P still want to know it all?

Yes i want to know, it doesn't bother me much about spoilers in that quest.

OK. First cicada shows some legs - go to Rock Troll Lake and look at the heel of one of the still-standing legs in the middle of the lake.
Can't recall about the 2nd one.
Third one shows a pair of branches in a V along with dotted lines - go to the areas outside Dumaas castle (I think the southern edge of windscream grove) and on the TOP of one of the hilly areas you'll find a similarly positioned pair of sticks. Follow that arrow to the opposite hill and you can see the orange scarab brooch on the tree.

After using the brooch on the locked box on the island, it shoots up a flare and the fourth cicada letter directs you to the gazeebo with a telescope, on the winding path, north of the Sunken Ruins lake.

Then some silent cicada (irony) gives you some bad attitude about being called out of hiding rofl.

have a clue in google with "cicada marked # 2" in a forum like this but wrote by japanese, you need to tranlaste a bit and theres a pic, i think you know that place, cicada 3 is between the lake near Potaria with small island, cicada 4 is the house, not really a house in the spiral way, and at the cicada 4, you will get a request for waitting cuz its developing quest.
BTW, you should try to learn some ninelives language. its not really hard but not easy to remember. the climbing club can give you something usefull for that.
good luck and have fun