What does the higlighted symbol indicate ?

Answer 1

[Ngonidzashe Nedziwe]

those a signal logging probes. You can use them to log the signal passing through that section on to the workspace. you can remove or add more by right clicking the line segment and selecting properties form the pop up menu list that appears.

[Ngonidzashe Nedziwe]

you can find more information on signal logging from this link https://www.mathworks.com/help/simulink/ug/configuring-a-signal-for-signal-logging.html