Tinted Lens doesn't really affect his Special Attacking prowess, as he gets quite a few coverage moves, and it is only good on not very effective hits. Psychic/Psyshock and Air Slash give it STAB, while Energy Ball, Flash Cannon, and Shadow Ball can provide coverage for you. Dazzling Gleam is also great for Dark types. Tinted Lens is best on Pokemon that only use one type of attack. If you want him to only have that one attack, then don't give him Psychic, as Dark types will still wall you.
Personally, the best way I have found to use Sigilyph is Magic Guard with the Flame Orb as the held item. This is a fairly common set for Sigilyph, but I have swept teams with it:
Sigilyph @ Flame Orb
Ability: Magic Guard
EVs: 252 HP/252 SDef/4 Def
- Stored Power
- Cosmic Power
- Psycho Shift
OK, Dark types still wall him, but at least you can burn them. Alternatively, replace Psycho Shift with Miracle Eye if you are really worried about it. I prefer to deal with Dark types before sending him out, though. After a couple of Cosmic Powers he is near impossible to take down, and burning Physical attackers makes them completely useless. Stored Power will reach an insane power after several Cosmic Powers, and so even resisted hits will hit like a truck.
Back to Tinted Lens, like I said I think there are much better options for Sigilyph.
As &Psychic x pointed out, I should probably also mention the Pokemon that work with Tinted Lens. I think the best options for this ability are Yanmega, Venomoth, and Mothim, as they can all use STAB boosted Bug Buzz, which nothing is immune to, and use their other moves for support (Quiver Dance, Defog, Roost, Protect, etc). Butterfree can as well, but it would need to give up its 97% accuracy on Sleep Powder (courtesy of Compound Eyes) to do this.