This may be kind of silly but it has helped me as I’ve studied for the SIE. Its a simple little mnemonic that’s easy to remember & quick to write down, taking the thought out of which secondary market is what:
1-L-E (Listed, Exchange)
2-U-O (Unlisted, OTC)
3-L-O (Listed, OTC)
4-i-E (Institutional, ECN)
Basically all I do is remember “LULI” and “EOOE”. Like i said, kind of silly but takes the “thinking” out of the secondary markets questions. Gives you a little more time for the harder questions! 
4 Likes
Great mnemonic, I love it - thanks for sharing!
Here’s another silly version 
Subdivisions of the secondary market
- First market
- Listed stocks trading on Exchanges
- Second market
- Unlisted stocks trading OTC
- Third market
- Listed stocks trading OTC
- Fourth market
- Institutions trading through ECNs
4 Likes
It’s not silly - it’s great! Thanks for sharing! 
1 Like