Matori

Well, technically Equity has nothing to do with all these kinds of securities...

Equity is simply Asset less Liablities, which is the basic FR rule. All kinds of securities are an asset on the balance sheet. So if you have more assets all else being equal you will have more equity. The connection is that any unrealized gains from HFT and AFS securities will bypass the income statement and come into the balance sheet as Other comprehensive income, which is a part of equity. So if you have an unrealized gain on HTS, that will increase equity.

MS are mainly relevant when you are calculating balance sheet ratios, as it's a part of current assets. (so a part of all curren/quick/cash ratio)