I cannot speak for everyone, nor claim to have the best method, but I can share what I do, as well as continue to express the importance of direct contact with them, which everyone can do, despite perceived shortcomings.
First, when you have their sigil, this is like they are "next to you" in a sense. You can pull their energy into you and connect this way, or communicate messages. Similarly, this focus on them allows them easier access to you, in the present moment or at a later date.
Relationships are like two-way exchanges of not just information, but also energy. See a synastry chart for a visual example of this. Therefore, your chakras can directly connect to the energy of their sigil, such that pulling their energy into your heart chakra facilitates love, through the throat chakra facilitates communication, and the 6th and 7th facilitate sharing of feelings and visions. Each chakra has a specific function, including the lowers, but the higher are more important for communications.
So this goes beyond just sending of messages, but also allowing them closer access to your soul, through which a full relationship can build. By becoming familiar with them on the level of a soul-to-soul bond, you can better sense them beyond just words.
This is also very useful in cases where people feel lonely or abandoned, where words alone will not do justice.
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As for their reply, sometimes you may sense this during this connection, or there may be a delay as the signs manifest for you. Sometimes, I will have a thought about a god and then directly after see an answer to my problem or concern. In this way, I know something has been communicated to me. Full astral hearing is not always necessary here, but rather openness to them and their energy.
You can also chant their names into your chakras and affirm the connection has strengthened. Do this, or pull their energy into your 6th chakra or hearing chakras, and this will aid your reception of their messages.