An initial pseudostate belongs to a region.
An initial pseudostate is shown as a small solid filled circle.
Symbol in context
When a state machine is started, initial pseudostates are searched in all regions of the root state. This search then recursively continues in each state that is a target of a transition whose source is one of the previously found initial pseudostates.
Interpretation of and deviation from the UML specification
There is no interpretation of and deviation from the UML specification for a state machine's initial pseudostate.