Perform only one, but describe how to deduce both? Understood.
I stand in front of my Sensei, with a big smile and instantly see this as a mistake... They proceed to punch me in the center of the ribcage and send me back due to the degree and nature of the technique used.
"Hey... What's the big idea, huh? Sorry for getting a bit close, but seriously... Why punch me like that? It's not like you have anything to fear... You're obviously an accomplished Shinobi, why would I dare give you reason to hit me? If you're worried about me using anything against you, please... Don't. Besides... Why would I hurt you so early in our session? It will be duly noted not to get too close to you, but seriously..."
Seriously... That hurt... Okay... Don't get to close, and you don't get pummeled... Easy enough to remember...
I start by focusing Chakra in my body and release it, using it to place you under an Illusion. It will alter your view on the world and create what appear to be self replicating clones, that attack using Kunai, Shuriken and various other Ninja tools. They don't physically attack you, because they lack any form to do so, that's why they appear to throw tools, I am throwing the tools in conjunction with the illusion to give the appearance of multiple (Shadow or other) clones. These clones are used to divert the target's attention away from the user and trick them into fighting the illusion, wearing themselves out, leaving them open for the user to deliver a final, fatal strike.
This illusion is somewhat easy to deduce as Genjutsu. If there are a bunch of clones in front of you, that can easily overpower you, yet they only throw Ninja Tools, it's easy to assume that the enemy is using Genjutsu. Also, the fact the clones appear to replicate when struck, at least to my knowledge, is unique, except in the case of Pain's Summoning Dog. That combined with the fact they don't physically attack should be more than enough to let one tell they are in a Genjutsu.
For the other Jutsu, it's easy to tell it's a Genjutsu. If the user is still visible to the enemy, and they perform a throwing motion, yet a Shadow Clone advances instead of a Tool, the target can safely assume they are under the enemies influence. Why would the enemy perform a random throwing motion, in the same direction of their clone? It's silly to think that they did it for laughs.
I hope this reply was adequate. If it wasn't please say, and I'll do it again.