Don't let the preparation work you've done for an interview be Top Secret...so that maybe the interviewer might understand all the work you've done. But probably they won't.
As part of your interview prep you are going to be visiting the company's website and social media. So whilst you're doing that, grab some screenshots and print them out.
Now, use these print-outs to make your notes on. Highlight some sections. Underline the key information. Use coloured pens and markers.
Identify the three things that you want to be your answer to the opening question, 'What do you know about us so far' and, using a marker pen, write them as bullet points on one of the print-outs.
Now you haven't got to try and remember anything as you have it written down!
Put the sheet in a folder...it doesn't matter whether its a cheaper card one or a flashier leather one.
When you open it and the interviewer sees your notes on the prints-outs from the company's online spaces, well it's obvious that you have done the grafting before this interview.
It's a great way to quietly make the point that, "I have taken this seriously....and I am a candidate worth spending time with."