is there any support for subactivity or the rake symbol

Question

http://www.holub.com/goodies/uml/

 

Subcase (Sub-Activity). The "rake" symbol indicates that the "activity" is complex enough to merit its own activity diagram. In use-case analysis, this is a "subcase"---a stand-alone activity that occurs in more than one use case but is not large enough to be a use case in its own right.

Answer 1

A work-around is to use the rake symbol (I found an icon and made a sprite from it using the PlantUML tool) in an activity, and then do another diagram. 

@startuml
sprite $rake [16x16/8] {
0000000000000000
0000000jj0000000
0000000jj0000000
0005555jj5555000
000jjeejjeejj000
000jj00jj00jj000
000jj00jj00jj000
0000000000000000
}
start
:Identify security problems <$rake>;
stop
@enduml

@startuml
partition "act IdentifySecurityProblems" {
    start
    :Step 1;
    :Step 2;
    stop
}
@enduml

Answer 2

I know the question is quite a few years old, but I stumbled on it with the same question. That's why I will answer for others who might have this question.

I was unsatisfied with the grayscale sprite, because it doesn't scale. So I wrote a SVG rake:

@startuml

sprite $rake <svg width="16" height="16" viewBox="0 0 16 16">
<path
    style="fill:#000000"
    d="M 7,1 H 9 V 7 H 15 V 15 H 13 V 9 H 9 V 15 H 7 V 9 H 3 V 15 H 1 V 7 H 7 Z"
/>
</svg>

start
:Identify security problems <$rake>;
stop

@enduml