What is the difference between using a sigil for a regular purpose, and then using a sigil with a servitor? If I am correct, the sigil and the servitor must be put together to create the entity. What confuses me, is that the process in which one creates a sigil for the desired effect is similar to creating a servitor without actually visualizing the entity as a spirit body. Perhaps this confusion arises that I do not completely understand sigils, nor servitors but it would be pleasing to find an end to this confusion. Every time I attempt to create a sigil it always ends up being a servitor, and when I attempt to create a sigil I can't seem to complete it successfully because I do not understand what it is used for other than, metaphorically speaking a phone number for the servitor.
One names and represents an object, force, event, etc. whereas in the other context, one represents, and names, a personification. For example, a symbol can represent wind as just the wind or a symbol can personify the wind and thus work with a servitor of the wind that pushes the wind around. The act of personification determines whether or not it will be a servitor or simply an object that is manipulated. So, in this example, one could seek to manipulate the wind with a sigil that represents the wind which is seen as that, and not an entity, or one can see the sigil as naming an entity of the wind which is manipulated. If you intentionally treat the sigil as corresponding to an object that is not conscious, then you should stop having that issue. Personifying it thus creates something in the form of that personification thus yielding a servitor. How servitors and sigils are associated in your head is probably impacting how you think about them causing you to unconsciously think of every sigil as a possible servitor thus making it into one. The difference lies in how you treat it, use it, think about it, and the context. Like how a word can mean something entirely different in a different context.
Really, it is all an extension of yourself. Think for a moment of having a dream. Everything in the dreamscape is an extension of you, but a chair in a dream may be treated as simply an object though it may mean something else versus a person in the dream which is represented, acts like, and is treated as a person, though, in reality, it is the same as the dream chair. Edit
The most obvious difference between a sigil and a servitor is the participation of the magician and the effect aimed at itself. If it is a one-time act, then a sigil is more practical. However if it is a continual process thaty needs to be done, then a servitor can be employed, thus allowing the magician to worry about other things.
Sigils and runes can correspond to properties and attributes meant to imbue an object and thus grant a continuous effect making it so that it is better for more than a one time act without the magician having to participate beyond setting the spell in say, for example, an enchantment.