We have investigated the visualization of safety information for mobile crane operations utilizing transparent displays, where the information can be presented closer to operators' line of sight with minimum obstruction on their view. The intention of the design is to help operators in acquiring supportive information provided by the machine, without requiring them to divert their attention far from operational areas. We started the design process by reviewing mobile crane safety guidelines to determine which information that operators need to know in order to perform safe operations. Using the findings from the safety guidelines review, we then conducted a design workshop to generate design ideas and visualisation concepts, as well as to delineate their appearances and behaviour based on the capability of transparent displays. We transformed the results of the workshop to a low-fidelity paper prototype, and then interviewed six mobile crane operators to obtain their feedback on the proposed concepts. The results of the study indicate that, as information will be presented closer to operators' line of sight, we need to be selective on what kind of information and how much information that should be presented to operators. However, all the operators appreciated having information presented closer to their line of sight, as an approach that has the potential to improve safety in their operations.