Many web sites include a dark bar at the top of the screen that will show the user's signed in state. This is commonly dynamic and will change depending on whether the user is signed in.
This is the case for stackexchange.com and all StackExchange sites.
Some large online services present a static equivalent of this on the main marketing site, showing only 'Sign in' regardless of whether you are signed in. The 'Sign in' option will take you either to the sign in form if you are really not signed in or will take you to the relevant application if signed in.
This this case for Google Analytics. When I visit https://www.google.com/analytics/, there is always a 'Sign in' option regardless of whether I am signed in.
This is also the case for Go Squared. When I visit https://www.gosquared.com/, there is always a 'Sign in' option regardless of whether I am signed in.
From an engineering perspective it is easier to present a static 'Sign in' option and then either take the user to the sign in form or to the relevant application as required. Doing so makes the caching of the relevant main marketing site so much more straightforward.
From the user's perspective (based on personal experience only), the static option is a spot confusing in cases where I believed I was signed in. Google Analytics catches me out like this more often than not.
I would have expected that the dynamic presentation of the user's signed in state would have been the better user experience choice as it reduces the risk for confusion and reduces the risk of the user taking an incorrect action as a result of any confusion.
I would then have expected the above-mentioned online services to have opted for a dynamic presentation of the user's signed in state. And specifically in the case of Google Analytics I would have expected Google not to be able to solve any related caching concerns.
Is there a currently-accepted best practice in this respect? Have there been any publicly-published usability studies that support one choice over the other? Are there any noted conventions that support one choice over the other?