The markings that shifters receive after coming out of their titan forms have stayed relatively uniform throughout the run of the manga.The marks are relatively shallow in nature and have some physical shape that coincides with the shifter in question. For example, Reiner has more angular shifter markings that represent his titan form rather well.
With this in mind, It’s only in few instances really that the markings radically change. Chapter 72 marks one such occasion. Bertolt’s marking are radically different compared to previous occasions when he has had his marks.
Although this change might be a purely aesthetic one for no other reason than aesthetics , it’s rare for rather uniform designs to change in this manga. It’s also rather interesting to compare the instances in which Bertolt has had his marks as shifter markings only really change when shifters have endured a lot of physical stress.
This most evident example of shifter markings changing in appearance occurs when Eren’s face is ripped off in Hanji’s experiments in Chapter 51. For what little of Eren’s face we can still see, we can see the markings are incredibly deep, much deeper than through regular strain through regular use.
With this in mind, let’s go back and compare the instances in which Bertolt’s markings appear.
The first instance these markings appear for Bertolt occurs in Chapter 43 after a long battle with the scouting legion, in which he burns much like a candle in his colossal titan form, and then takes a 50 meter dive bomb off the side of a Wall.
This all occurs in half of his titan form and his markings are long, thin, and much more similar to the markings that have appeared in the manga prior.
In Chapter 72, we see Bertolt’s markings through Eren’s thoughts, but it is interesting to note that Bertolt’s markings are much, much deeper, even skeletal appearing in some places, and his appearance is closer to that of his Colossal Titan form.
This instance is supposed to be indicative of Bertolt’s transformation at Trost, and during this instance, Bertolt has merely maintained his form for a few minutes, kicked a gate, and pushed canons off the wall.
Despite a relative lack of energy spent and seemingly less energy used than during the Clash of the Titans arc, Bertolt’s markings are closer to that of a shifter who has spent an enormous amount of energy. A reason for this might be that maintaining the full Colossal Titan form overall uses more energy, even if only used for a few minutes.
If this is true, it helps prove the popular, long repeated theory that Bertolt can’t maintain his Colossal Titan form for very long and that his titan form might have a longer cool down period. Even more troubling is the idea that it might be easier for Bertolt to lose himself in his titan form given these restrictions as hinted by Hanji in Chapter 51.