Here's is an example for her website on what her markings look like in 1 Peter 5:
While I follow Kay's method, mine doesn't always look like hers! Here are a few tips to keep your bible looking streamlined/readable while still marking key words:
1. Choose "normal" markings. I often underline in different colors (like blue for author and orange for recipient), double underline (in green for locations), circle words in different colors (and sometimes highlight the center of the circles), and put boxes around words (like red for warnings and blue for instructions).
2. If you use a picture/marking, make it small and manageable. For Divine terms (God, Jesus, Holy Spirit), I use the three triangle points to make up the Trinity (using a purple pen). God is the top of the triangle (sometimes it looks like a hat), Jesus is the right side (and I intersect the line to make a cross symbol, like Kay's picture above in verses 10 and 14), and the Holy Spirit is the left side (usually forming a "cloud" above the word "Spirit"). Sometimes I use a stop-sign symbol near passages with warnings, or a Jewish star for passages about Israel. I like using the conclusion symbol (three dots in a triangle shape) around words like "therefore" or "so."
3. Don't feel like you need to mark every word. In fact, the point of marking is to not have many words marked so the important ones stand out more. I don't always mark references to God, key figures, or locations. Key words like "love," "faith," and "prayer" are only marked in sections of the Bible that teach about those things. In epistles, I don't mark every reference to the author and recipients, but only the primary ones (greetings, warnings, specific facts).
4. Make use of lists. As you can see in Kay's picture, she made a list about Peter. Instead of marking every reference, I make a list of references and narrow it down to a few things I learned about the person (word, event, location) and add the short list to my Bible. Then, I mark any significant passages where it is a key word or used multiple times (indicating a lesson or teaching).
5. Do what works for you. At the end of the day, do what works for you! I often print out a copy of the book or passage to mark first (for my study). Once I work through each chapter and have a better grasp, I will mark my Bible appropriately. You may want to mark everything in your Bible, or just keep a notebook on the side with lists instead of marking your Bible, or a completely different method altogether!
Just remember: Marking your Bible is a tool to help you dig deeper, not a shortcut to understanding or applying the passage. Make it work for you!