Those initiatives may be useful because they provide information. However, the problem is that there is no standardization. It is done on a voluntary basis. Some may decide to use a logo and others not, which can create disparities between certain foods.
A food item with a logo might appear healthier than the one beside it which has no logo. But the one without a logo may be just as nutritious. If a logo had to be adopted, it would need to be applied systematically to all foods, rather than everyone having the choice of whether to use it or not.
So it may be a useful tool, but the process would require some thought and some oversight using standards. The labelling would have to be systematic and standardized.